are you saying running them both simultaneously? I've done it accidentally without issues but don't know if there could be issues. but you can use both on the same computer. I do that all the time. I have clients that I provide support for that are still on 2019 and others on 2020. never seen any problems.
I've got 2015, 2017, 2018, 2019, 2020, and 2020 public beta installed on my machine. I have the older versions on account of not uninstalling/removing when adding new versions, though I haven't actually needed any of them in quite a while. Switching to a new computer any day, and then ... yea, I'll lose probably all before 2019.
But yea, you can have multiple versions installed simultaneously.