Hello there

I'm (still) a beginner in need of guidance and I hope you can help me.
Last year I did RTK until ~1800 but my laptop broke and dumb me didn't have backups online (which I regret deeply now!). At the time I was also drowning in work because of my graduation thesis and I left japanese completely behind.

Now I want to restart- should I do RTK again from the beginning?

Yep.

I had an (unintentional) break of about a year after reaching 600. I started from zero, and it only took a couple of weeks and I was back on track. Relearning those kanji will refresh the primitives that you'll need to continue on, and it won't take long.

Personally, I'd just start up an Anki deck or use the SRS system here, and see how it goes. I've take long breaks in the past, and still remembered a lot. You can configure the SRS to give longer intervals for remembered cards, at least in most cases, to limit unnecessary reviews.

If you're doing RTK to learn to write the kanji, then yes, you should redo it; if you're using anki, I recommend suspending anything you remember easily (I'm not sure how the 'bury' function works, but that might be a good option as well).

However, if you're just doing it to help with vocabulary acquisition (which is also a good reason to do RTK), you might should just go ahead and start working on vocabulary; you can keep up RTK on the side (the above advice still holding), but by 1800, you should be pretty much set on being able to see kanji as more than just scribbles.

Personally, if I was in this situation, I would go with the second option, returning to RTK when I wanted to practice writing.
It's all up to you, of course.

You can just start over. The cost of starting over isn't as high as you'd expect, anyway (when you already know a card, reviewing it goes very quickly, so you lose very little time).

You'd have to do almost as much work if you had the backups, and it would be more frustrating than just starting over.

Thank you so much for all the help!
I'll be restarting it.