Windows 10. I can't stand Cortana & it's just run slower & slower with bloatware with every update. It feels like it's a never ending game of wack-a-mole with me fixing unwanted changes to my settings, security or updates. Windows 11 is probably going to make me snap when I am finally forced to switch, going by Win10 in recent years.
I don't care for the subscription junk for NSO, as I'd like to be able to just play my $70 Switch games online without paying an additional fee to do so, especially when it's multiplayer only? That feels super cheap with Splatoon 3, anyway.
Bit niche but I also dislike Bandai upgrading to rechargeable batteries on a lot of their new virtual pet products I collect (Digimon, Tamagotchi). It seems fun at first, but after 2-3 years it won't charge as well, & I can't just replace it like I can a battery. Once it's done, it's done, & these newer chargeable pets have been expensive from the start, or limited products online JUST because of that feature (yuck). I still have 20 something year old Tamagotchi that work just fine with plain 'ol school batteries. I just prefer it over the convenience of charging. Not to mention a ton of people in my collector groups already have reported charging ports breaking off the boards, cords overheating or devices failing. Scary stuff for us collectors.
Not regret per se, but I do remember trading in my DS lite for a 3DS as a kid along with a few games. I did miss how the lite looked and felt but apart from that it was primarily an upgrade. It was the games that I regretted trading, pretty much just MKDS and NSMB for their respective 3DS counterparts.
Pretty much any significant PC upgrade (in this case going from a Ryzen 7 5700x to a Ryzen 9 7900x). I just recently upgraded my CPU, which meant upgrading my motherboard, my RAM, and my PSU. That process meant having to diagnose a bad PSU, ordering a new one, and then discovering that my motherboard was also bad. It turned what should have been a two hour long process into a several day long ordeal.