I'll describe the issues I've had with the PS5 since I got it on launch day.
*Major issues:
-Console completely shut down during a Miles Morales playthrough. After reboot the console would give no video or audio, but would send my TV intermittent signals (My TV would switch to HDR constantly). Disconnecting and reconnecting cables and power cycling did nothing. I could boot into Safe Mode. Rebuilding database did nothing. Restore to factory settings did nothing. Fully resetting the console with a new firmware file from Sony's site did nothing. On my very last attempt I booted into Safe Mode again and selected to boot in 1080p mode. This did the trick. After boot, I tried changing the video setting to 4K, and the issue happened again (Screen went to black, no audio). I imagined the video chip on my console was busted and unable to display 4K anymore. A day before sending it back to Sony I decided to try and set it to 4K again, and it somehow worked. The issue has not happened again since.
*Minor issues:
-While my account was open, my brother decided to create an account of his own. After creating the new account and switching to it while mine was still opened, the OS slowed down to a crawl. The console would either not react to any commands, or perform them several seconds later. Everything was slow as molasses to the point it seemed the console was frozen. We decided to delete his account for now.
-My NVME-to-USB enclosure (Asus Strix Arion) was not compatible with Rest Mode, asking for repairs and closing my games after waking the console up. I decided to switch to another enclosure with an ASM2362 chipset and it works perfectly.
*Game related issues:
-While playing Spider-Man: Miles Morales, the game began to perform extremely choppy after a Fast Travel. The game would seem to stop to load every 3 seconds or so. Easily solved by closing and restarting the game.
-Loading the game from Activity Cards will lock you to the suit you are currently using, unable to change it. Easily solved by starting the game normally from the dashboard.
So far that's pretty much it. Since I received the console I have not experienced any game crash (Except for the one I mentioned in the first section), no weird error codes, no nothing. I've been playing several PS4 games from the external drive without any issues whatsoever. Seems like my console is somehow pretty stable (Hope I'm not jinxing it). The disc drive can get loud, but only for a few seconds. I can't hear the fans at all, and I have not identified any "coil whine" or any other weird sounds (well, except the normal sounds of plastic cracking due to heat expansion and stuff like that).