If you wish to cancel the membership of the Steam beta program, then pursue the given instructions.

Users of the Steam beta have said they have solved the program by canceling the beta program. Doing that, launch the software of the Steam client.
You should click on the Steam menu on the upper left-hand side of the screen of the software.
Then choose the Settings on the menu.
You have to select the Change tab for beta participation at the Account https://bit.ly/2WHvPTt
Choose the option ‘Opt-out of all beta programs’ at the Beta participation drop-down section.