I'm experiencing this issue…
I'm experiencing this issue on my 2024 Crosstrek. I bought it new with the standard mirrors and paid the dealership to install the upgraded auto-dimming mirrors with approach light. Upon receiving my vehicle I noticed the issue and brought it back to the dealership to fix, which they were unable to. The dealership informed me that the mirrors were "performing as intended". I lodged a complaint with Subaru who worked with my dealer to replace all of the mounting hardware and mirror components, and the issue persists (though slightly less severely). I'm hopeful that Subaru will do the right thing and develop an actual solution and fix my (and other's) vibrating side mirrors.