I was using Evernote v 10.3.7 build 458378 public, Editor: v111.0.14414 and Service: v1.22.6 on MacOS v10.15.7 and this morning 2020-11-12 I experienced the same behaviour with no syncing or rather the effect of seeing what you wrote in a new note just disappear. Everything worked yesterday but today things did not.
I took your advice and installed the Evernote Legacy version Version 7.14.1 (458325 Direct), Editor: 69.3.10951 (15add1e) and on this version syncing works as it should.
I do love Evernote and have been a Premium Member for a year or so, but as of now I have so much info saved/synced in Evernote I cannot afford new Mac-versions with "surprise features" like this. I will keep using the Legacy version until I am sure that this bug is ironed out from newer versions.