Apple Numbers has Stopped Saving my Work

Numbers isn't saving my work. i'm using Sequoia 15 on an iMac 2019. i've been getting messages that i can no longer collaborate in iCloud due to my machine being as old as it is.

i've been having problems with Numbers not saving my work lately.

Regardless, i thought i could work on my desktop and save as i would any old file, but it seems not. i deliberately saved my file last Sunday locally but when i opened it up today all the changes were gone. The file on iCloud also failed to have any of my revisions. i made a pdf of the file and uploaded it to iCloud, so i could verify that in fact i had made changes not saved.

What is going on here? Do i have to stop using Numbers?