Oh God you just noticed that. It happens all over the net and Roku....everywhere!
The commercials are always louder I guess to drive it into our heads to go out and spend our money on **bleep**. Like dried up jellyfish for our brains<<< ironic aint it?
This used to annoy me a great deal a long time ago.
Not sure what happened but a long while back I started using computer speakers THESE .
And I either got used to it or I dont know.
You can make a Feature request but I doubt it will fly.
Volume Leveling is something usually built into a TV or Sound System.
https://www.techwalla.com/articles/how-to-level-the-volume-on-a-tv-when-the-commercials-come-on