I have been doing tactics training quite regularly since the beginning of the year. However, I haven't really been playing a lot (for obvious reasons). On average, I would say that I spent 10 hours per month on tactics since January (except for June, as I was really busy with other things). I also did some additional training in other areas of the game, but that was limited to mainly 2 months. Now, despite my efforts, I don't think I have improved. Chesstempo estimates my rating between 2150 and 2250 Fide (for context: my current rating is about 2100), but I don't see that in my Blitz games (I have been rated between 2200 and 2300 on lichess since January with almost no change. If anything, I got slightly worse). I find that pretty discouraging, and I'm wondering if all that training has just been a waste of time because I didn't play OTB games. There a lot of other things I could do with my time and I'm honestly thinking of dropping chess completely if all my efforts are in vain. Any help is appreciated.
Thank you for sharing your very discouraging story. I've been an IM for years and recently I've tried to become a grandmaster, did a lot of tactics but: I failed, and now with corona and 0 OTB games it feels a bit silly anyway. So I started to learn code, which is fun haha and very off topic here.
The biggest difference you can make to get from 2200 to 2400 is understanding of pawn structures and having a coherent repertoire. Especially facing 1.Nf3 and 1.c4 becomes more important. But apart from a broad coherent repertoire I would say start learning openings 20 moves deep, and in case you have some forced line, start memorizing 30 moves, take research seriously, try to get some great books to guide you. And then in the main lines, try improving on the book.
Another great help is to take Dvoretsky's endgame manual and go through it a lot. That book is pure gold. Especially online a lot of games end in some kind of endgame. And making rabbits appear out of hats is great.
The reason for focusing so much on openings is because that's probably your bottleneck right now. You don't have the strategic insight to make your tactics work. e.g. different players need different things. Try to identify where you're weakest.
One trick to do that is to study the topics you most dislike in chess. For me that was opposite coloured bishops, and that has helped me a lot getting better at positional play.
You can still do the tactics, but I am 100% sure you would regain your motivation when you would work on something you need more!
Last but not least: chess progress is a bitch! The rating always comes too late, when you lost motivation and think about quitting.