CraigB, I just replaced all the vent caps on our 2019 3791RD. Our attic vents looked just like your pictures, so much so that when I first saw the pictures I thought "I don't remember posting them".
Here's the ones I ordered on Amazon for the mushroom vents:
https://www.amazon.com/dp/B074JFP3PP...roduct_details
$14.99 for 2 of them
and here's the other vent caps:
https://www.amazon.com/dp/B09BC7J4F7...roduct_details
$15.99 for 2 of them. I had to order 2 sets (total of 4) since I needed 3.
The big mushroom vent caps just unscrew off. The smaller vent caps have a screw holding them on. Once it is removed, they just pull straight up. The screw was under some silicone on mine.