After recent update from macOS Mojave to macOS Monterey, lost all my music from MacBook

Why oh why... you probably messed things up, when all you had to do was to migrate your account, and all the music, photos, etc would be right where they should be, ready to use.

You don't want a full install, but you can easily run Migration Assistant, select the user account and migrate that.

If the username.

Here is what I suggest:

1) Create a new admin account - let's just call it 'admin'

2) Logout from your account, and into the admin account

3) Delete your "normal" account (this is to avoid later duplicating stuff that you have copied, and also to let you reuse the same username)

4) Start Migration Assistant, select your Time Machine drive, and then check ONLY the user account(s) that you want.

You will be running Monterey, with all your documents, photos, music, mail ... and preferences just as you had them before.

It looks like you got bit by the nasty "available" but not "free" space.

In recent years, macOS has gotten into the habit of not immediately freeing space when you delete things.

Select the drive in the Finder, and press Command-I.

What does it say in relation to available space? I am guessing that a great amount of space is "purgeable".

For example mine has some 20GB "purgeable".

It turns out that it does not readily release that space, and there is no guaranteed way to force it.

Anyway, if you see some 300GB of "purgeable", that is the reason it then (annoyingly) it says there is not enough space.

But try restarting in Safe Mode, and see if some of that space gets freed.

anotherNeoLuddite wrote:

i tried a ‘start over’ with time machine six months back (with TM being on mojave and mac on catalina at the time) and all **** broke loose, so am a bit hesitant to try this, but many thanks for the suggestion nonetheless!

A VERY IMPORTANT caveat: when you "start over", you should really migrate ONLY the user account(s), and not other things (not applications, not settings, not "other files").

This is particularly relevant when doing a "big" upgrade (a few versions newer) or after one has already upgraded in place, year over year. The problem, often encountered in these forums, is that one may have stuff from, say, 2014, and after a sequence of upgrades that old stuff may break.

I have seen many a report where people still had silverlight, flip4mac, flash and other really old stuff.

It does take a while after migrating to reinstall some applications, but you will avoid all that **** breaks lose.

And also get a cleaner slate going forward.

If you still have the TM backup & didn't ruin it, I'd start over then use Setup Assistant to restore everything.