1. Within your firewall settings, make sure
these ports are not blocked:
UDP 27000 to 27015 inclusive (Game client traffic)
UDP 27015 to 27030 inclusive (Typically Matchmaking and HLTV)
TCP 27014 to 27050 inclusive (Steam downloads)
UDP 4380
TCP 27015 (SRCDS Rcon port)
UDP 3478 (Outbound)
UDP 4379 (Outbound)
UDP 4380 (Outbound)
UDP 1500 (outbound)
UDP 3005 (outbound)
UDP 3101 (outbound)
UDP 28960
It could be easier to temporarily disable your firewall during steam updates.
2.
Steam > Settings > Internet > Internet Connection Speed:
an incorrect speed value may take a long time to download all the updates.
3.
As often recommended by Steam support, close your Steam client delete the "ClientRegistry.blob" file in your Steam folder. Start Steam.