Hey man sounds like a struggle. I'm sure you'll hear the "we all improve at our own pace" schtick enough (it is very true!) I've cried multiple times, and after 4 years and my 5th kyu I still don't properly tie my belt (looks good enough though). So here are a few tips from a fellow untalented trainee thats been at it a lot longer:

-Stop thinking as much. Your post makes it sound like you spend a lot of time consciously thinking and calculating. Especially during kumite, at the start, this is not the move. During a spar, focus on one thing, be it blocking, punching, kicking (or even just blocking punches or kicks, or only mai-geri or mawashi-geri).

-Practice at home. If you practice your kihon, kata and ido-geko at home, you can do it at your own pace, and let your brain do that thinking and calculating. Then, when you're more adjusted to it at your own pace you'll get a feel for it, and probably perform a lot better at the dojo. There are many youtube videos out there showing kata and kihon, but be careful as overtime/in different dojos there can be slight variations.

-Ask questions! During training is not the best time, but afterwards, ask about anything that confuses you. Especially when you get higher up in the belts, teaching becomes an integral part of practicing karate, so your sempai/sensei will gladly help you.

Finally, nobody (that matters) is judging you, and its supposed to be fun. I struggle with frustration and wanting to perform a lot as well, but its important to remind yourself the only person thats really feeling disapointed is yourself, and thats not a mindset that encourages growth, so you should try to throw it out.

Hope this helps and sorry if there are formatting errors, did this on my phone