@Ozymandsss I’ve been reading through your post and I believe your issue may be drivers. I know you checked your drivers already, however sometimes windows requires other audio drivers not related to Realtek updates that can cause weird little issues.
I would grab something like driver booster, just google it and grab the free version. It scans your pc for outdated drivers for every component including your audio devices,usb ports,motherboard,Ect. I can’t promise but I do believe this should crush your audio issue.
Hopefully it works but I’ll be lurking around so I’ll also jump back in to help