Strange experience on "refurb"

Bought old Lenovo T460s to play around with various distros.

Came with Windows 10 and bum battery. (Fuggit! That's a refurb?) So I bought/installed a new battery

Then tried to upgrade to Windows 11 just for giggles. No dice: message that device didn't meet minimum requirements. OK

Put on Linux Mint for dual boot as easiest. Played around. Worked fine but I've never adored Mint

Decided to try Debian next. Installed fine over Mint in partition

But then everything became gawd-awful slow: nothing hangs, but response time for everything is sad sad sad. Couldn't get wifi working. Left machine alone a while. Reboot didn't help. Finally gave up: live and learn, y'know

A day or two later, I take another look at Windows to see if it's slow too. Well, now WTF! it has already upgraded to Windows 11 which seems to work fine at normal speed

So I reboot into Debian. First thing is: wifi is up automatically. Everything is running fine: no terrible delays

Go figure. Maybe I should be suspicious