@Sheree
Hi, and welcome to the forums.
I've been using Macs for the last 28 years and currently on Catalina 10.15.4 (latest) with CrossOver 19.
It would be wise to backup the Mac Mini and do a clean install of Catalina, instead of an upgrade.
Depending on the Mac Mini's hard drive, backing up to an empty 500GB or 1TB external drive would do.
Backup software not required either, just copy the whole Mac drive to the external. Then get a coffee.
After that, upgrade to Catalina with a clean install. This will erase the Mac Mini completely during install.
Once done, it will present you with the loading sequence as if the Mac Mini was brand new.
Then put back only the apps and documents that are required, then update to CrossOver 19.
Most Apple apps will have new versions, and won't need to be copied from the backup.
DO NOTE: That older 32-bit apps won't work on Catalina, and newer replacements will be needed.
If you're not sure, reply with a list of apps that are required, and we'll figure out what to do with them.
This may seem drastic, but it will clean any clutter that may have accumulated over the years.
Also the Mac Mini could have at least macOS 10.8 or 10.10 on it, which is 8 or 6 major OS updates ago.
Do also write down your Wi-Fi and password for the startup sequence. You'll setup a new user account.
Ask any other questions too, as I've been through the pain of upgrading my Macs over the years.
Hope this helps in some way.
--mike