Can't seem to recover lost reminder list

A personal nightmare just happened … I was working on my Mac (on Ventura 13.5.) when suddenly one of my reminder lists in Reminders disappeared – literally in front of my eyes!

I am not sure how, but I may have accidentally deleted it with a random finger move. It happened so fast that I can't tell for sure.

The first thing I intuitively went to do was to press Command + Z (undo). I did it multiple times, but I could observe no reaction from pressing it (that's why I doubt I've caused the issue in the first place).

So when I saw I couldn't undo it, I immediately went to disconnect my iPad and my iPhone from mobile data and wifi. Thankfully, my iPhone hadn't synced yet, so the reminder list was still there.

That list is of high importance to me and contains many reminders from the past that I need to keep for documentation. I never thought of backing it up because it's in iCloud, and that's where the backups are supposed to be done by Apple.

So on my iPhone (still disconnected from the internet), I thought I could try to add a new reminder to that list, and also change the lists name, then maybe this would "update" the list in some way and hopefully make it reappear on my Mac and iPad, but sadly it didn't work out. As soon as my iPhone connected to the internet, the list disappeared from it, and of course it never appeared on the Mac or iPad.

(I took screenshots of the list before connecting the iPhone back to the internet. A mistake, now I need to type it all. And I forgot to screenshot the checked reminders on top of that.)

I tried restoring data multiple times on iCloud.com with various backups Apple offers you, but the reminder list was never restored. Even though it existed at the date of all backups.

In fact, this data restoring feature has created an even bigger mess. I believe more reminders are now missing, and some checked reminders from months ago are now unchecked, even though they definitely weren't unchecked at the time of these backups. And the individual order of all reminders is lost as well, making it hard to orient oneself.

Something else I noticed (maybe linked) is that I still have the option to upgrade Reminders to a new version in all Reminders apps (on Mac, iPhone and iPad). The new reminders are then not compatible with old reminders, Apple says. I have an old Mac Pro I've used until a month ago or so that wouldn't be able to upgrade. I removed it from my devices now.

When I press those "Upgrade" buttons in the Reminders apps (which I've done plenty of times on all devices), it would re-load all reminders in the app, and it almost seems like for a second, all lost reminders would be back, this time including the lost reminder list. At this point, all lists would have 0 reminders and you could slowly observed how they're being loaded and the numbers increase.

At the end however, the lost list would have disappeared again, and the displayed total number of reminders would have decreased from maybe ~650 to 550, so basically it would go back to the same state as when I'd restore data on iCloud.com

I thought my issue with the lost reminder list may be linked to this "upgrading" (as they call it) of the Reminders app.

Who thinks there's still a chance to save this reminder list + all its checked reminders? Who knows how? Has someone else had or seen this issue?

Is that list maybe stored somewhere on my Mac? (I sadly don't have any backups)

Thanks for reading. This is so important for me to fix. Thanks in advance for the help!