The cache folder is not safe to delete, at least not all of it. There are pages online discussing this.
I know for sure that cache/themes is safe to delete.
Have you looked in
modules/Accounts/Accountvardefs.php
custom/modules/Accounts/Accountvardefs.php
The actual construction of the custom fields depends on a few things, this is all documented in the Vardefs and Extension Framework chapters in the Docs.
There is also a database table called fields_meta_data, but normally you don’t go there, you just edit the Vardefs and run a Quick Repair and Rebuild, then scroll to the bottom and it provides a button to edit the tables for you.
But if your experience is that it is safe to delete, I take that as evidence
And I suppose that some of these things have changed since the SugarCRM days… for example, “cache/upload” is now “upload”, and everybody knows it shouldn’t be deleted (well - only some parts).