Many Apple Stores are still closed or running on limited hours due to COVID. It may be hard to get that help right now
What OS is the computer currently running?
Are you aware that some older apps will not run under Catalina? It requires 64-bit apps and cannot run older 32-bit apps. Check your "must have" third-party apps. Office 2019 and Office 365 are fully compatible, but Office 2016 must be updated via Microsoft Auto Update BEFORE installing Catalina. Office 2011 and older are not longer supported by Microsoft and cannot work with Catalina.
IF you use Adobe Creative Suite apps, check your versions with Adobe to see if they support Catalina.
Although sometimes incomplete due to a lack of reporting, this third-patry site helps with version compatibility:
https://roaringapps.com/apps