Is that a personal account or an organization's SSO account?
In case of doubt: SSO is when you use an account by your organization (like university or company) and login with your organization's credencials.
I use Zoom with SSO through the university at which I teach. This is a Pro account, but with a certain limit of concurrent licenses. So it is possible that at some point the number of people connected through this account reaches the number of available licenses and then if more people connect they get Basic mode.
Sometimes, after a while, I see that although I'm visibly signed in with a Pro account, privileges seem to be declined, as if I were in a Basic account - the most obvious sign being meetings cut off after 40 minutes. On those occasions, usually by clicking the account and choosing Sign Out, and then logging in again, it is resolved.
This seems to happen more in my afternoon, and it may be related to the issue above.
I am afraid that I can't help with the virtual backgrounds. I have a few but never use them, as I feel that unless the user has a green screen, it is just not worth it. Zoom tries admirably, but the results are still poor, and I don't blame them. I don't want parts of my head to disappear, or my arms to be invisible when I do handwaving.
I just tried it now. I don't remember having to download anything, and I did use (if only as an experiment) virtual background before. It did ask me if I wanted to download the Virtual Background Package, I clicked Download and it did not even asked for any password...