You don’t have to downgrade. Visual Studio 2019 and 2017 run side by side. Installing Visual Studio 2019 installs a new application in a different path. It doesn’t upgrade VS 2017, so there’s no reason to downgrade.
I’m using VS 2017 and VS 2019 on the same machine for about 6 months now without issues.
solved Can you downgrade from VS 2019 to VS 2017