How much longer for support for catalina?

What exactly do you mean "support", do you mean how long will it get updates? We cannot speculate on these forums, however based on past releases of Mac OS I would say until at least 2 generations after Catalina. For example, High Sierra just received it's last updates right before Big Sur was released. High Sierra is 2 generations older that Big Sur. So that would be at least another 2-3 years.

Probably the only updates we'll be seeing for Catalina over the next year, maybe two, are security updates. They are finished with tweaking the system.