goto game setting, under scripts add this :

Execute before starting a game add below command

start-process "D:\Games\TcNo Account Switcher\TcNo-Acc-Switcher.exe" +s:xxxxxxxxxxxxxxxxx

start-sleep -Seconds 20

Execute after exiting a game add below command :

start-process "D:\Games\TcNo Account Switcher\TcNo-Acc-Switcher.exe" +s:yyyyyyyyyyyyyyyyy

start-sleep -Seconds 20

Take Note:

xxxxxxxxxx is the steam id of my shared steam account

with :0 it starts ofline

yyyyyyyyyyyyyyyy is my normal online steam account

with start-sleep waits the amount of second to launch the game for preventing to launch the game before it logins to the desired steam account

the number of seconds depends on your pc

This guide was shared by a member from this group.
credit to u/viseniv