Ah. Well it seems to be really Sandisk’s fault then:
it isn’t Windows that’s causing the problem but rather preliminary firmware versions on certain SSDs. These unfinished firmware versions, which were never intended for end users, appear to have been triggered by the KB5063878 update and thus began causing the problems described by users.
And I guess a bit mine. I updated all the drivers directly from my PC’s website, except from that one, because it was an upgrade and I didn’t know SSDs had firmware.
Then again, the SSD was sold to me brand new with a prerelease config. Yeah, I’m still blaming Sandisk. Sigh.