How to uninstall LibreOffice from Mac OS Catalina?
For any app that comes with an installer package, check to see if there is an uninstaller option. 

Check with the developer, to ask what step they recommend for removing the app.

Otherwise, for most apps, delete the following:


the .app bundle from /Applications. 
subfolders with the app's name in /Library/Application Support and
&lt;user&gt;/Library/Application Support


There may be subfolders in the company's name, e.g. Adobe.

If you want to go mad, you can also look for folders with the app's name in other subfolders of the user Library:  Caches, Containers, LaunchAgents. They may be named as com.company.appname, or org.company.appname. 

There may be files in &lt;user&gt;/Library/Preferences, of type com.company.appName.plist. Typically these will be only a few Kb, and if you miss them (or other small files in other places), they will do nothing but occupy one-hundred-millionth of the space your hard drive.

Essentially, this is all that so-called 'cleaner' apps do: search for files with the app's name in your user Library. They can of course delete the wrong thing and miss obscurely named files just as easily as you can. 

Orphaned files left over will just sit on your hard drive and never be read. (Ahhhh.) They won't affect the running of your computer in any way.