In the past I liked to make clean upgrades of macOS, meaning I erased the boot drive of my Mac and installed the new version of macOS to an empty drive.
I don't do this anymore. This year I upgraded my MacBook Pro to Catalina running a system with Mojave.
The reason why I'm not doing this anymore is practical: too much additional work. If I would do a clean upgrade, I would have to copy all my dot folders to my new system, install all the applications I use, copy most of the folders in the home Library folder, install Homebrew etc. But I don't want waste my time with unnecessary work.
I was listening to MPU where David and Stephen said that they don't make clean upgrade. So I asked myself: why am I not doing the same? So I did the mentioned upgrade and there were no issues with the upgraded system (or the upgrade process).
Speaking of Catalina, it is not a version of macOS that Apple can be proud of. Perfomance-wise it is not bad but it seems to me that my 2016 MacBook Pro worked a little faster on Mojave. High Sierra was awful for me on the MacBook Pro, so much high-load CPU cycles and too much beachballs. But on the other side, I had no performance issues with High Sierra on my 2011 iMac .
No mather how you do the upgrade of macOS, please make a bootable backup of your system you want to upgrade. You can never know what can go wrong.