I need some people that had the same problem with me, and fixed it on their own or with other people. My friend is talking and nobody hears him, and he does not hear anybody else. His mic is not muted it says he is talking on his screen but nobody hears him and other people do hear me. But they don't hear him, i have already tried everything in https://support.seaofthieves.com/hc/en-gb/articles/115012749647-Windows-10-Chat-Settings
Voice Chat problems
This is a hit one.
It could be:
-XBox family settings to protect children from others. Was the case at my account, i had to activate the right setting to talk with others
-could be your device. If you have multiply devices for sound (bluetooth and cable) SoT is a little pain in the sea. For me, i deactivate every soundsystem i dont need while playing. Because it doesnt understand my headset and speakers.