fantastic Howard that a simple clean solved your problem, but I'm afraid it will be a different story for those of us with sd card reader problems.
The problems are not down to dirt.
How can I be sure? In order to avoid data loss on the sd card, my 'genius' idea was to gracefully unmount the card either through the Finder or Disk Utility. The OS, however, has different ideas, and randomly re-mounts the sd card, only to dump it again when it is bored of it, and then send me a message that *I* ejected the card, without unmounting it first, which is not good practice. No ****, sherlock!
Monterey is buggy as **** - for many tasks, like, say, opening a new window in safari, it feels like I'm on a 2010 era HDD macbook pro, not a speedy ssd mean machine. High sierra was snappy as a snappy thing, and it's back there I'm heading.
It's almost as if apple are causing these problems and slowing down our machines in order to nudge us towards new hardware, doesn't it? I've sung the apple hymns and waved their banner through (very) hard times and good for 30 years, and this crap stinks.