The bug I never fixed isn't a bug in code I wrote, but rather an OS problem I've given up on fixing.

I dual-boot Windows and Linux on my desktop PC. Every time Windows updates, it switches from grub to the Windows bootloader, making it impossible to boot into Linux. I've fixed it three times (each time requiring a different fix, from disabling fast startup to reinstalling Grub from a live USB), then gave up. My desktop PC is now a Windows machine. I'm upgrading some parts soon (including replacing my boot drive with an NVMe SSD) so I decided when I do that, I'm just going to reinstall Linux on the new drive and see how long I can last without installing Windows at all.