Multiplayer does not work on current version but I found a workaround. It seems like there is a problem with Among Us sending ICMP ping which requires "cap_net_raw+eip" privileges on linux.

Using information from this blog post https://churchman.nl/2019/03/14/granting-capabilities-using-capsh/ I run following commands:

export -p > ./savedenv
sudo capsh --caps="cap_net_raw+eip cap_setpcap,cap_setuid,cap_setgid+ep" --keep=1 --user=$USER --addamb=cap_net_raw -- -c "source ./savedenv; rm ./savedenv; steam"

Now I got working multiplayer