Enable Chat/Voice in CS2 Casual Mode Servers

The reason it works in competitive but fails in casual is due to a specific quirk with how CS2 handles the "Mute All But Friends" setting.
When you play Competitive, the game automatically forces your teammates into a temporary "Party" for that match. Because of this, the restriction bypasses them, allowing you to hear and type to them. In Casual, players are not put into an official party, so the game actively mutes absolutely everyone.
To completely fix this, open your developer console (~) and look closely at this exact setting:

The Instant Fix
Type this command into your console and hit enter:

cl_mute_all_but_friends_and_party 0


Use code with caution.
This forces the setting to completely turn off, clearing the red lines and opening up communication across both game modes.

What else to check if it persists:
If the red lines remain, check your menu settings directly to ensure a secondary restriction isn't clashing with casual lobbies:
1. Navigate to Settings (Gear Icon) > Game > Communication.
2. Verify Mute All But Friends is explicitly set to No.
3. Change Mute Enemy Team to No (Casual allows you to talk to enemies, but if this is toggled "Yes", they will stay blocked with red lines).