My MacBook Pro does not show accurate SSD memory usage.

regardless of exactly how accurate/inaccurate that display is, you need to find an additional way to store some of your 'stuff". You just have too much for the size drive you have now.

An external drive could be used to store your older Photos, or your entire Photo Library, for example.

--------

A very small contributing issue is that this data comes from Spotlight Indexing, which is really good at adding the sizes of new files, but not so good at removing old ones. But even if you compute a new spotlight index, it does not solve the fundamental problem that you have too much stuff for the size of your drive.

How to rebuild the Spotlight index on your Mac - Apple Support

.

There isn't a 'fix'. Just ignore About this Mac > Storage. As one example, "Documents" is just those files your Mac thinks are Documents. It's not your Documents folder. As you can see on mine, the About this Mac reports 24.37 GB while my Documents folder is 18.68 GB according to Finder Get Info. The latter is the real size.

I had 70 until last night, and now only 13,19GB.

Probably you should have led with that...

Regardless, go to Finder, select your internal drive (Macintosh HD), then File menu > Get Info. If it shows that you have 13.19 GB available, then that's correct. The problem is not inaccurate display of available space, it's something else. A download. A wireless iPhone backup. Bottom line, as Grant Bennet-Alder states, you need have too much stuff and need to remove some.

70 is not enough when MacOS requires over 9GB free just to start up. You have too much stuff.

Try to find a new place to put things. Just eliminating a few items or even ten percent does not solve the issue, just put it off.

Which is why I suggested...

neuroanatomist wrote:

...I personally use the free utility Disk Inventory X to see what's taking up space.

Doesn't matter what program you use, really...the point is that About this Mac > Storage is not the way to go.

About this Mac > Storage is basically unreliable. Use Get Info in Finder, or I personally use the free utility Disk Inventory X to see what's taking up space.