I created a new theme using the Theme Generator and uploaded it to our tenant via PowerShell. I can also check it with
Get-SPOTheme. I cannot, however apply this to an existing site collection, I don't even see it under "change look".
I tried with 2 brand new site collections (team site - classic and also a publishing portal), none of them worked.
How can I make the new theme available? I watched tutorial videos and, according to them, this is the way it should work.