Anything like a Rubic's Cube

I spent a six week period around Christmas rocking in a corner playing a bubble pop game on my phone over and over.  It was the only thing that would calm the anxiety.  Not a lot of math's in that, though...

Might give those a miss then...

These wooden puzzles and models require good modelling skills and materials - the wood is not great quality so needs a lot of sealing and micro-repairs as the build progresses.   The middle parts of the ply break out and needs reassembling to make the gears mesh properly.

Not tried it myself yet but very tempted to get one of these. Could end up hurling it across the room though.

Search Amazon for cluebox, 2 models available.

Also how about computer games - eg something vast and deep like Stellaris ?

There's a lot to learn, and when I'm feeling depressed it helps "take me out of myself".

I'd recommend a mid-range Technical Lego model - whilst being a construction kit, there's a lot of pleasing maths behind the design - lots of triangles and mechanisms - some are motorised 4x4 jeeps with working suspension.       There's a lot to learn.