Mounting an SSD that had Ubuntu installed before as an external drive doesnt load anything

Solution 1:

There may be nothing at all wrong with the drive. It may not be encrypted… but Macs can't read Ext4 without 3rd party software.

There's a freeware option FUSE, but it's always been unstable, so YMMV.
If you have Homebrew installed, then FUSE is accessible with

brew install --cask osxfuse
brew install ext4fuse

Alternatively, I'd recommend Paragon's ExtFS for Mac

Further info - MakeTechEasier: How to Mount and Access Ext4 Partition in Mac