Can anyone give me any advice on how to remove these imperfections?Im using oil base gloss varathane.I used 120 grit sand screen between coats, wiped down and tack rag the floor.Most of my floor is perfect,It’s just the doorway entrance that has almost all of the imperfections.I brushed a 6x6 area,so I’m guessing that I dragged particles from my knees out of the entrance.Any way to fix this without another coat? Thanks!!

Is your finish freshly opened as a new can?
Poly will start to harden inside a closed can. First way to notice is a film on top of the finish, but hardening already has started when it is exposed to air. The poly starts to harden and tiny clumps are made which will seem like sand when this finish is spread.
It may not be dust, but grit from older poly-urethane stored with air above it.
I use this type of poly for the first coat only sine it will be smoothed by screening.
If this is the case, you will need to screen and coat again with fresh oil modified poly-urethane.

Yes, it is a freshly open can.I did some experiments before I saw this post. I sanded 400 ,grit then 1000 ,then 4000 then car compound and topped it off with polish compound.
Wow,the amount of energy and work that was put in Compared to the end result was not good.The high ends of the grain are dull(satin) and the low ends are glossy.During sanding I noticed that most of those bumps were air bubbles.
I would like to ask you;Do you strain your poly? Should I use a different product than Varathane? The oil base take too long to dry…Should I just go with water base if I’m fully sanding the floor .Do you have any poly recommendations?Thank You

After the floor is sealed and you like the color, you can wait a while and coat over the poly with water-based poly. Some people like it better than regular oil based poly-urethane. I think it wears better, but there can be minor scuffing so the floor will get dull in traffic areas. The first coats of the finish already down need to be cured before you screen with 150-220 grit then vacuum, tack and coat.

I've never been able to get a completely dust and air bubble free finish coat, didn't matter which finish i used or what applicator i used i think it's just the nature of the material.

On a high end job we would strain brand new pales of finish, because you never know. Vacuum and then tack it twice. Before we even went in there to do final cleaning our clothes should be clean, separate pair of shoes for inside and outside. Not the most fun process