A couple of things.

My hotpoint has the ability to "rotate" the exhaust fan.

Why?

There are 3 installation methods:

Vent outside (straight out the back)
Vent outside (straight UP)
Vent inside (recirculate) (out the front)

The fan assembly can be rotated so that it points in one of 3 directions:
(which matches the venting the vent method of course)
back or "up" or front
Aka, there are 3 ways it can be installed, only ONE is correct for a given installation of course.

If your assembly isn't installed (rotated) correctly, then it will run, but won't be effective.

I definitely can feel my fan out the front (on my recirculating setup), even on low.

............

How to debug?

Unfortunately, you'll have to pull the microwave down to check it.
And that is easier done with 2 people.

Pull it down, unplug it. Remove it.
Set it on a table.
Plug it up.
Check the fan (it is located at the top/rear/middle on mine)

Mine had a single screw that I could remove so I could "rotate" it.

Pulling the assembly out wasn't super easier..because of grease buildup.

If you remove the assembly.........UNPLUG THE MICROWAVE.
BE CAREFUL, but be FIRM when pulling it. Watch for the wiring so you don't pull it out (damage it).

If you get it on a table, you should see if it was setup properly.

An installer could have not rotated it correctly, thus it makes noise (runs), but isn't effective.................

Good luck!

It'll make sense when you have the unit down off the wall.

.......

The fan-assembly "cube" has one side that is open.........aka, where the air can escape.

Imagine a box fan (the 20" kind you can buy at target/walmart for $20).
If you wanted a box fan to work (to bring air in from the outside), would you:
A. lay it flat on the ground pointed at the floor?
B. attach it flat against the ceiling pointed up toward the ceiling?
C. put it in a window and point it "in" so the escaping air is coming into the house?

The obvious answer is C.

That is same common sense approach you'll take once the unit is off the wall, and you're looking at the fan-assembly cube in the microwave. You can instantly feel how the air is escaping..........and it'll either make sense or it won't make sense.....like the box fan example above.

..............

It sounds more intimidating than it is. Just get the microwave down and onto a table...............and it'll be very easy to debug and determine if that's your issue.

Recirculating is 180 degrees from the rear/wall exhaust. Aka, the air is blowing toward the front of the unit.

...........

Do you have a charcoal filter installed in the unit? Reason for asking is because I have a GE over the range and for the first 10 years I owned it I did not realize it requires a charcoal filter in the output duct when used in recirculating mode. The fan/exhaust performance was fine, but all it did was recirculate the same air. The steel mesh filters you see from the underside are grease filters. I also observed that over the range MW, do not do a good joob of venting the front burners of a cook top and do a much better job over the rear burners. They other thing to check is if you do have a charcoal filter, it may be clogged or your grease filters may be clogged.