When I went back to mtb after a layoff, I switched to flats on doctor’s orders. It’s weird at first, you’ll probably need to relearn some things (or rather, learn some things that your spds have let you not bother to learn). Good news is, this is worth doing whether or not you stick on SPDs, you can carry technique from either pedal back to the other.
I think on balance I preferred spds but there’s really not much difference, and what there is is mostly out at the extremes (frinstance, really strong riders can use them to pedal harder- for most people, that just empties the tank faster. And yes you can pedal more easily in rough stuff but that doesn’t come into play til most people will have stopped pedalling.
So yeah, give it a go, you might hate it or you might love it but if you give it a good try and figure it out properly, you’ll likely benefit. But the first wee bit might be shaky, don’t be put off!