Hello there, new to the forum and I hope this is the right section to post this,

I recently felt like replaying Freelancer after a (very) long time and decided to reinstall it since my old install was not functional anymore.

Everything went smoothly until I tried to activate the "Just For Fun 3.0" mod, I end up getting an error and the mod doesn't activate.

The error message is as follows :

Error: FLMM has determined that 'Just for Fun Mod V 3.0' won't properly activate.
Error: Solar.xml:410: Unable to find dest 'docking_sphere = berth, HpDockMountA, 2, Sc_open bay' in 'D:\Freelancer\Jeu\Freelancer\DATA\SOLAR\solararch.ini'.

If anyone knows how to fix this, I thank you in advance.

Note : I already tried the "standard" steps I could find online (uninstalling Freelancer and deleting all files, reinstalling the game, the SDK and everything) and it did't work.

If the mod is a scripted mod then it looks for specific text strings in the game files and if it doesn't find them will fail to activate. So, if you're using the wrong ini files you'll have problems. The mod, if it's well written and documented should let you know which SDK or file updates it's written for.
Most use Adoxa's JFLP files or the original vanilla game files to run.

If the mod is set up to just replace existing ini files with the modded files it should work unless the destination files are protected in some way.