Fluidmaster 400A fill valve: very slow toilet tank fill
Cleaning out the valve should help. On the other hand, a new 400A fill valve is about $7.50 and it will take you under 5 minutes to replace your existing one (water off, slide the retainer ring up, pull the old valve, throw it away, put the new valve down at the same height, click the retainer ring back down, re-attach tube to overflow, water on).

I'm pretty sure any pro would just replace the valve to save time.