Only thing I can think of is the Logitech MX, wanted a compact mechanical keyboard to be able to take to work (was hybrid one day a week in office at the time), just ended up utterly hating the switches/travel distance and sending it back. They have their audience though, just my preference.
Otherwise it's stuff years ago that's cheap, when e.g. Friends or parents used to buy whatever was the cheapest instead of a little research.
I generally go try stuff or at least proper reviews as I don't buy tech that often. Galaxy watch 4 classic I borrowed and realized didn't work for wrist.
Other one would be Pixel watch 3, that one isn't really regret, I think the watch as a smart watch is great, prefer the old tizen notifications to left, but otherwise great watch, just not my style, more a regret it doesn't have proper watch crown / rotating bezel.
Not sure if really counts as tech, but only thing I can think of that I purchased was a midi piano keyboard, was too cheap. Actual feel of keys with step/resistance is too important, but was compromise as 100 EUR vs 1000, will probs get a proper end of year as I miss playing.