I think I've tried everything you've suggested, to no effect.
You could try clearing sto's cache/logs/prepatch folders as sometimes, they will get corrupted and cause issues like this.
I tried this, but it didn't appear to fix anything.
OP: Download your display drivers. Remove them, and reinstall your display drivers.
Done.
Which GPU do you have?
Intel Iris Xe
Also, make sure vertical sync in turned on.
I've turned it on in both the Intel settings and the STO settings.