I just tried to run PS CC (2019) and it wouldn't run, saying I should re-install. I noticed there was a update and then saw I have PS 2020, but it won't run..instant crash. When I look at CC, it tells me to do two updates (20.0.5 & 21.0.1) but both fail to load.
When the CC client show you thast you have updatres for version 20 and 21 it seems that you have installed both version on you computer. This matches also with the message that you should do an reinstall of PS 2019.
Try to deinstall both versions and then install the appropriate version again. If this doesn't help I would recommend a clean reinstallation by following the steps below: