Arduino Nano programmer not responding anymore

Hello everyone!

At first I should mention that English is not my native language, so I apologize for any wrong words/usage of grammar etc. beforehand.
Also, I'm relatively new to microcontroller programming.

I'm currently working on a little project involving the FastLED library, some WS2812b LED stripes and a Arduino Nano. Initially, it was easily able to upload any changes I made in my sketches but since yesterday evening, uploading sketches are nearly impossible.
I've been using the Atmega 328P (Old Bootloader) option from the beginning and everything worked fine and I could upload my code to my Arduino without any problems, but I wanted to add the finishing touches yesterday, so I plugged in the Arduino to my laptop (I only have one USB 3.1 port on this thing and that worked before) and tried to upload the sketch. Uploading took way longer than usual and didn't succeed eventually. I closed the IDE (Arduino 1.8.13, hasn't been updated since I started working on this project) and restarted it, tried again, it didn't upload again. I pressed the reset button on the Arduino and tried again, didn't work either. I plugged it off of the computer and tried again a couple minutes later and suddenly it worked and I could upload my sketch.
The problem is, everytime I now want to upload the new sketch to the Arduino now, it doesn't upload (but deletes the old sketch at least partially because when I plug in to the LED stripe, it doesn't do anything anymore) at first and after restarting it, I get the following error messages:

avrdude: stk500_recv(): programmer is not responding
avrdude: ser_send(): write error: sorry no info avail
avrdude: ser_recv(): read error: access denied

and after a couple more tries, I can finally upload the sketch.
But it gets increasingly more difficult to do so and actually, I want to add a few lines of code to my sketch but I'm afraid to do it because the last upload took about 30 minutes of trying again and again and I was worried that I had fried the arduino but it still gets recognized everytime I plug it into my computer.

Has anybody ever had a similar problem and was able to figure out what it was and how to solve it?

Does the same problem occur if you try uploading to just the Nano alone, without any LEDs or any other external circuitry connected to it?

Yes it does. I don't have anything else connected to the Arduino while uploading sketches. I did not change anything about that either.