Thought it could be a warped disk, but would I not experience shaking/vibrating when braking? I am not experiencing that.
I'm definitely no expert, and your right about the vibrating, my Mini had a warped disc and had an awful vibration from the wheel and a juddering noise when braking however my thinking would be it depends on how warped the disc actually is, I can hear the squeak in that video and it does seem to be braking related. If it ain't the pads then there isn't really a lot else going on other than the disc, never had to change a disc on a golf so I have no idea what the setup is on a golf but I know on my mini even some dirt between the hub and disc or over torqued bolts when mounting is enough to cause issues. Maybe jack up the car and try rotating the hub to see if you notice any friction, in my case the warped disc wasn't free running and made contact with the pad for a quarter of a turn unlike the other side which was free running.
When I had the disc off and placed it on a smooth surface then it was extremely obvious as the disc wouldn't sit flat and rocked about, turned out to be a good thing in my case as I upgraded to vented grooved discs and ebc greenstuff pads which actually make the car want to stop now instead of feeling like the engine is doing all the braking.
and for some context I'm 25 and have never drive a car older than 2010, so a classic mini felt completely hopeless on the brakes to me haha
Hope you get sorted soon zainahmed48, they say a unclean discs and pads can also cause squeaking but if you've cleaned them also to me it's probably not something that's going to cause any real issues but I know if it were me I couldn't leave it alone either as my ocd wouldn't allow it lol