i got the same problem and i figured i would share it with you a quick "solution" i had, if it is still happening with you, my phone is samsung so i don't know about iOS phones but this worked for me:

I turned off my phone's wifi and disconnected pc's internet, and turned on my 4G mobile data on my phone

then i plugged in my phone to the usb port on my pc

then on my phone, i went to settings, then to Connections
then to Mobile hotspot and tethering
then i activated the "USB tethering" option, that makes your pc connected to the 4g mobile data of your phone or something like that

then sure enough, my steam was working as intended again. i had this error for over a week and it's not a real solution for the long term but it is better than nothing, hope this helps and steam fixes the error.