Try using a hairbrush, pet hair roller, etc. to remove the lint.

I read that cotton items produce lint in the washing machine while polyester items pick it up. Much like you've discovered :(

They should have been washed separately.

The only thing I can suggest is a fabric shaver. I've used it for pilled things. Not sure how it would do with lint.

Here is a link to just one but if you Google fabric shaver you'll get more options.

Here is a link that might be useful: Fabric Shaver

My best advice is never buy polyester blanket again im experiencing the same thing with this comfortor i bought a few months ago and every time i wash i have to use one of those lint piller machines and it just sucks having to do that everytime so next comforter i buy im checking the material lmao cuz idk what else to do

I would run the fleece blanket through a rinse cycle then toss it into the dryer. Clean the lint filter of the dryer when you've finished. If all else fails a soft pet brush should do the trick though it's a little tedious.