Samsung S7 speaker phone not working (at all)

My Samsung s7 (SM-G930F) works for making calls on 'normal' (non speaker phone) mode in all apps. but whenever i switch to speaker phone (regardless of the app i am using) the other side (the person I'm calling) can't hear me anymore. As soon as I switch to non-speaker-phone mode the other side can hear me again. It also doesn't work in video calls (the other side can't hear me when video calling). Note: voice recorder also works just fine.. Note2: with headphones installed (via headphone jack) it also works (other side can hear me just fine) I've tried the following: - reset to factory settings - clean microphone/speaker port+holes - checked microphone connector (if it was properly installed, it is) - cleared cache partition in android recovery menu (no change) - tried it in safe mode (problem persists) - and countless other 'fixes' which unfortunately did not work for me... I have a custom ROM installed (I tried to find something as close to the stock ROM as possible). I previously had Lineage OS 16.0 Herolte installed but on that ROM Roaming did not work so that's why I decided to install a different ROM. Currently installed ROM I am not 100% sure of, will check tonight. I believe I followed this video tutorial so I should have the android 8.0 ROM installed from sammobile.com: https://www.youtube.com/watch?v=LvPL6hskf6w . On the current ROM Roaming does work. I believe the current ROM causes the issue since speaker phone was working on lineage OS previously. Are there any other fixes/tests I could try to determine/fix the issue? Any recommendations on where to find/download stock Android 8.0 ROM for the SM-G930F? Thank you!