There have been a number of issues with Notes in the past (some you rread) but there are probably too many threads to search through.
You, however, are so far behind that any issues and fixes have come and gone.
I am not on the latest of anything on my Teracube. /e/OS 1.14-r and Notes 3.7.1.
Not sure it’s fair to complain so harshly given the outdated nature of your setup (but at the same time I run older Android Oreo and Pie and expect them to operate “normally”). Though the sudden loss of notes would make anyone ticked off.
I am not sure of the possibility of restoring notes since they seem to be unavailable in the cloud.
Maybe check the following if you haven’t already.
Notes on phone that wouldn’t sync lost after OS update. Any hope of recovery?