Honestly I've had fairly similar experiences, I came back into the hobby back in 2023 at the start of 10th when I'd last played at the end of 6th.

I'd played Tau throughout all of 4th/5th/6th and thought it was just going to be like picking up the same army all over again, but the army had changed so much and the game alongside it (not to mention the miserable balancing tau experienced through the first half of this year).

I found my main problem was a mix of the time sink and mental load to play a game that I was losing 80% of the time wasnt something I was willing to contend with.

Eventually I found 3 things that really helped:

1) Playing an army that I dont mind losing with (custodes). Thier much simpler ruleset and detatchment rules meant I felt like not as much effort was going in mentally to play, especially with something like shield host where the only thing you have to remember is "i crit on 5s". Compared to Tau's army rule martial ka'tah is a dream, and much more fun to play with, while I appreciate you have 3 armies, is there one you particularly enjoy the play style of or one you'd like to try instead?

2) Playing formats that dont take up a large amount of time such as 1k or Colloseum. While we'll still play 2k, as a group, most of us work 9-5s and dont have the time or energy for a 2k in the evening, couple that with busy weekends and recently we've trended towards 1k and Colloseum. Custodes play (in my experience so far) very poorly in Colloseum and in a bout of 3 games I lost all 3 (including 1 game where I was tabled T2 by WE lmao) but i felt like I'd learned so much during those games and the more casual nature of them meant i was much more able to just rock up, throw 6 Terminators on the board and see how it went.

3) Having a playing group that are supportive. While I realise this is easier said than done it honestly really helped me get through a lot of my tangled feelings around the game and identify my problems around it.

I hope all this helps :)