Macbook Pro 13" 2020 M1 screen is black but backlight still working. Can use with external monitor but screen doesn't come on anymore.

About 6 months ago the screen of my Macbook Pro (13" 2020 M1) started just randomly cutting out and going black, I would turn it off and on again and it would be fine for an hour or two but then just cut out again, nothing seemed to trigger it. It happened more and more frequently so I quickly backed it up before it just stopped working altogether. Luckily I was able to keep using it with my external monitor and the webcam still works but the screen has not come on since. The backlight seems to be working and the keys light up but that's it.

I don't know much about computers but I spent about a month trying every single thing I could find in online forums and nothing worked, I eventually gave up and have since switched over to a Mac Mini but want to try to get this fixed so I can sell the Macbook or use it when travelling.

I did talk to someone at the Apple store who said my Macbook is out of warranty and it sounds like an issue with the flex cable, they didn't open it up but quoted me £400-£600 to replace the screen which is ridiculous and they said there's no guarantee it would fix the problem. I managed to carefully open it up today to have a look and I can't see anything glaringly wrong with it but haven't tried to take the screen apart since I don't want to accidentally damage it.

I bought it from new and had it for about 3-4 years with no problems, used it 8 hours a day for work and have never dropped it or spilt anything on it. The only thing I can think that might have damaged it (apart from if it is in fact the flex cable) is that I was using a caravan as a studio last winter and the temperature dropped below zero a couple of times so sometimes the Macbook would be so cold it hurt to pick it up but it never had a problem with starting up and by the time the screen crapped out it was already Spring.

Any help or advice will be very much appreciated, thank you!