Creative Cloud app allows me to upgrade from PS 26.10.0 to PS v27.1 but not to PS v27.0

There should always be options in the installer dialog to migrate preferences and remove older versions. That is the general update dialog and not dependent on version. Look again.

But first of all, I would check that the bug you're referring to isn't in reality caused by migrating preferences. 

Preferences are rewritten on every application exit and are prone to corruption by irregular shutdowns. Small errors will accumulate over time and carry over. Here's the thing: A new version will have partly new code, and so latent errors may unexpectedly surface to cause problems in the new version. Corrupt preferences usually look like application bugs and are often mistaken for that.

I always advise against migrating preferences for this reason and I never do it myself. Just make sure to save out your custom actions, brushes etc. first.

Also, be careful about removing old versions. The installer removes the old version after the new one is installed, which may break file asoociations. Leave it, and remove it later when you're confident everything works as it should. When you do, start with the newest and go backwards. Then reinstall the one you want. This is the safe procedure to avoid all problems with file associations.