Hi Ck. I'm Greg, 10 years awarded Windows MVP, here to help you.
I've not yet heard of Focus Session bothering anyone. But I do notice that for some reason I'm not signed into the Clock app even though I'm signed into Windows with my MS Account.
Perhaps if you sign out of that one app at the top of the settings it will back off. There shouldn't be any reason to sign into the Clock except to enable it to access your data for the Focus sessions which you do not want.
It bothers *me* anytime I open an app and it chooses to default to a setting I NEVER use just because the app's publisher is trying to push a new feature.
In this particular case, something meant to reduce distraction has become one.
I guess everybody wants irony, but nobody wants to pay for it.
Like CK, I'll be switching to a third-party app.