Fatal Error 'FMX.FlexCel.Core' not found.when compiling OSX after upgrading to 11.2

It seems like this happens every time there is a new Delphi version.

[dccosx64 Fatal Error] Main.pas(15): F2613 Unit 'FMX.FlexCel.Core' not found.
when compiling existing projects for OSX 64.

Reinstalling FNC does not help.

What is the fix?

FMX.FlexCel.Core is a part of FlexCel, not of FNC pack, so you should try reinstalling FlexCel instead. Does it still not work if you reinstall FlexCel?