S20 ultra, the other party on Phone can't hear my voice when I go to other app.

[Dr-SAYYaD]

Hello guys ! I am using samsung galaxy S20 ultra, it's been a month that I notice whenever I'm on phone with someone everything is good , but as I go to other apps , because i use other apps whenever I am on phone I open other apps to browse and also talk at the same time , but I can hear then good but they can't hear my voice. I tried everything even reset all settings, still the same problem . If anyone knows how to fix this please let me know, ASAP.. 

[HasanAskari]

Try keeping the call in a small pop-up screen through settings (I hope it's available in S20 Ultra as it was there in Note 20 Ultra that I used previously)
Further, if you use any other apps with the mic access, the mic and (speaker in most cases) can be used by one app at a time.
For example, disable mic permissions for your Chrome or any other app and see if it works.
You need to use a stock launcher with a stock dialer too.