OK, I think I found the issue:
1. After uninstalling PS_EventBus all upgrades failed. I could reinstall 1.7.7 (shared on this forum) but this version is too old for PS 1.7.8.8 and still won't allow upgrades.
2. I used a backup to extract the last version I had: 1.9.1 and zipped it to install it, but this failed as well! So I copied it manually over the existing 1.7.7 and changed in the database the entry under MODULES for the version from 1.7.7 to 1.9.1.
3. I tried to setup Google marketing and it seemed happy, so I also tried to upgrade a random outdated PS module (GDPR) and it succeeded.
So, NEVER remove PS_EventBus!
P.S. I tried to upload the ZIP with PS_Eventbus V1.9.1 but it always ends up with an upload error? (just 2.5MB)