Details for the issue

What did you do?

Following instructions in this tutorial, i tried to install the extension "mod_spatialite.dylib" for Mac 64 that is distributed via this Github repo in my DB Browser for SQLite (versions down below).
Went Preferences -> Extensions, clicked the "Add extension" button, navigated to the mod_spatialite.dylib file just downloaded to my desktop, and clicked "Save" button.

What did you expect to see?

Expected to get some message confirming that the extension was installed successfulky.

What did you see instead?

Dialog popped up w/ following message in red:

Error loading extension:
dlopen(/Users/walterludwick/Desktop/mod_spatialite.dylib.dyylib, 10): image
not found

NB: seems strange: that redundant .dylib extension is not in the path/file i selected... But so it was parsed by the machine.

Also: I ran the SQL script "SELECT spatialite_version();", thinking maybe spatialite was already installed, but no... DB4S returned the message:

Execution finished with errors.
Result: no such function: spatialite_version
At line 1:
SELECT spatialite_version();

Useful extra information

MacBook Pro running HighSierra (10.13.6)
DB4S Version 3.12.0, Built for x86_64-little_endian-lp64, running on x86_64
Qt Version 5.12.8, SQLCipher Version 4.4.0 community (based on SQLite 3.31.0)