I’m also facing this issue. Slightly different in my case as the issue seems to only appeared after Android 14 update. I can’t say for sure if it is directly related as I do not do handsfree calls every days. But that the only thing that come to my mind and I was able to have many normal conversations many months before (FP5 bought on march 2024).
Now my 3yo kid cannot be heard during handsfree calls (video or not, even with a normal phone call that does not use 4G/Wifi) despite literally screaming at the phone.
There is no issue at all without handsfree.
I’m also going to contact support. Could original poster follow the guidances on this page and add the appropriate tags to highlight this issue and this post ?