You said that:
I am giving away a shitty 128GB SSD, which was used with LUKS 2 for most of it’s lifetime.
This leads me to assume that it is not now? Is this the case? If it still has LUK2 on it, you can run cryptsetup-erase on the luks2 container. This won’t wipe any unencrypted data, though.
One needs to be careful and avoid block level wipes wherever possible for SSD as this will wear it out quicker. Obviously, if you have sensitive data unencrypted, you may have to. Shred is your friend, here. It works on entire devices as well as individual files. The individual files option is preferable if you the sensitive data is at known locations.
I doubt it. I think some filesystems have mount options that disable the journal for that session.