Does iCloud offer a feature to get back deleted files like Dropbox etc do? Hopefully your notes can still be found there...

Nope

Have you contacted Apple? Assuming you are using their notes app... Sorry I don't use an iPhone so I'm not sure what to advise here.

Are you using a Mac computer to sync Notes with your iPhone?

Have you performed a backup of your iPhone 12 to iCloud?

Notes are synced to iCloud but they don’t appear there either. :(

Could you check the "folders” of notes in the note app. In my iPhone, there were 3 souces of notes, one from iclouds, one from exchange email server and one from shared. I wonder if your notes were saved with different sources. 

Also, was there any other icloud account used in your iPhone previously?

I had a similar issue where I ‘lost’ notes on my iPhone 13 Pro synced to my MacBook Pro (I’m using Monterey, Ventura may have a different layout). On the Mac, I had to go into System Preferences and click on my Apple ID. iCloud Drive should be checkmarked. Next to that, click Options. Check if Notes is in that list and place a checkmark in the box. Initially, the Notes app was in the Options list and now appears in the main listing. 

On your Mac, click on Overview and sign out of your Apple ID, then sign back in. Make sure your Mac and iPhone are on the same Wi-Fi network. Open the Notes app on your iPhone and it should start syncing and adding notes to your iPhone. If you have enough storage space on your Mac, you can store iPhone backups locally instead of using iCloud.

Are you using a Mac computer to sync Notes with your iPhone?

Have you performed a backup of your iPhone 12 to iCloud?

Notes are synced to iCloud but they don’t appear there either. :(

I had a similar issue where I ‘lost’ notes on my iPhone 13 Pro synced to my MacBook Pro (I’m using Monterey, Ventura may have a different layout). On the Mac, I had to go into System Preferences and click on my Apple ID. iCloud Drive should be checkmarked. Next to that, click Options. Check if Notes is in that list and place a checkmark in the box. Initially, the Notes app was in the Options list and now appears in the main listing. 

On your Mac, click on Overview and sign out of your Apple ID, then sign back in. Make sure your Mac and iPhone are on the same Wi-Fi network. Open the Notes app on your iPhone and it should start syncing and adding notes to your iPhone. If you have enough storage space on your Mac, you can store iPhone backups locally instead of using iCloud.

Unfortunately mine is a Windows PC 

I’ve retired my Windows 11 laptop for a while now. Check Dinh’s suggestions and see if the links below contain useful information. Creating a backup of your iPhone should be a priority, especially before an iOS update. Perhaps someone else in the community can shed some light on this.

https://support.apple.com/en-us/HT212156

https://support.apple.com/en-us/HT209254

https://www.idownloadblog.com/2022/02/17/how-to-access-iphone-notes-on-windows-pc/

Are there any accounts that you’ve recently logged out of? One of the most common reasons that things like notes would disappear is because they were linked to another account that is no longer logged in.

Not that i know of … but maybe im not understanding the question. Can you give an example?

I think what he meant was that perhaps you might have your notes under (for example) "yourold@email" and are now logged in with "yournew@mailaddress" so that your notes seemingly disappeared?

Ahhh I see. I only have one Apple ID though so that can’t be it.

Try going to Settings > Mail on your iPhone. Take note of your Default Mail App (if visible). The Default Mail App field is not visible when using Mail as your default mail app.  Below that, Accounts shows the number of email accounts you may have. Tap Accounts. Tap the email account you want to check, if applicable.

If you’re using third-party email services like Outlook, Gmail or Yahoo, you can enable or disable Notes for each account. In the link below (view the first image), Mail (iCloud) and Notes are enabled for this Yahoo account example. In most cases, your Apple ID is also the primary email address of your Apple ID account.

https://support.apple.com/en-us/HT209254

On my iPhone, I’ve enabled Notes on a third-party email app/account. Mail (iCloud) is automatically enabled. You can change the default mail app/account by going to Settings and locating the app (e.g. Outlook, Gmail or Yahoo). Tap Default Mail App to change which mail app is the default.

I think this is what Allan M is referring to. If Notes is used on more than one account and you’ve logged out of one of the accounts, there is the possibility that Notes have disappeared due to being linked to one of those accounts. 

Ok is this what youre talking about?

Two accounts have notes enabled. See below.

Yes, that is correct. 

Have you backed up your iPhone at any point prior to updating to iOS 16.2?

I didn't manually back up my phone but supposedly iCloud is set to automatically backup?  In any event when I check my iCloud account (on my PC) it shows the exact same thing.  10 notes (of my original 142) 

On the image “Apps using iCloud”  tap on Notes On >. Next to Sync this iPhone, slide the toggle switch to the off position. Tap, Delete from My iPhone. Slide the toggle switch to the on position. I just tried this with 96 notes and they all reappeared. It took roughly two and a half minutes to complete. Your sync may take a bit longer. 

Is something supposed to show that this process is happening? (some progress indicator or something)  I just did it and I have no indication that this sync is happening? 

If looking at your iPhone, in Notes (Folders > iCloud > Notes)  there should be a small spinning spoked wheel. You should also see the note count increasing. On occasion, the progress indicator wheel will continue spinning, but the count seems stuck on a number. Let it go all the way to 142.

Well that didn’t work, all that came back were the 10 that were remaining after I lost the others. 

Are you logged into your Hotmail account?

yes

Is “On My iPhone” selected?

If enabled, this allows you to store messages locally on your iPhone, but those notes are not synced. The setting is found in Settings > Notes. On that same page, change the default account to iCloud. Try the Notes sync process again. The progress indicator is a rotating pinwheel. I couldn’t think of the word earlier. 

Another option is to sign out of your Apple ID, wait a few minutes, then sign back in. If still no luck, you may want to ask this question in Apple’s support community. I’ll keep looking for other possible solutions. The last update should have fixed this bug;

iOS 16.2 “Fixes an issue that causes some notes not to sync with iCloud after updates are made”

https://support.apple.com/en-us/HT213407 - near the bottom of the list. At the bottom of the page you can start a discussion in Apple Support Communities or contact Apple Support.