Hi All,
Just wanted to share my experience with this. I have a 2021 Plaid and early on the smell began on just the most humid/rainy days but over the years got worse until the smell was present almost all the time. Blecch!!
Replacing the cabin air filter didn't help at all, so after reading this thread I removed the HEPA filter and you could smell the funk in the filter itself. After removing the HEPA filter, I did the 14x20x1 house air filter mod and am thrilled to report that it worked!! Huge thank you to the members who suggested this!
Before sliding the filter into the now "HEPA-less" housing, I added about an 8-10" strip of "Duck" brand adhesive-backed weatherstrip foam on either side of the cardboard filter "frame" to take up the space that was on either side of the housing. Smell is completely gone and I can enjoy my car again!
For those wondering, I did try the service request route. They just wanted to change the cabin air filter and call it a day. In the chat they also suggested running the heat on high for 30 minutes. I'd done that a bunch of times and it didn't help a bit.
Thanks for reading and hope this helps!