Since KB5066835 on Win11, HTTP/2 is broken
(and so localhost is broken too)

https://www.bleepingcomputer.com/news/microsoft/windows-11-updates-break-localhost-127001-http-2-connections/

When you save on the steam cloud, Steam uses HTTP/2.
Because KB5066835 has broken it, save fail, and steam try again later, and again later, and again later, unitil he decide to tag HTTP/2 not available, and then it save by HTTP/1.1

If you have lot of file, save on cloud can take an hour, instead of be on an instant.

If you want to fix this, you can :
- Uninstall KB5066835, or
- Disable HTTP/2

Uninstall KB5066835 :
Easy to do, but win11 will try to install it again later.
And, this update fix lot of vulnerabilities (and 6 zero-day)... it's better to keep this imo.

Disable HTTP/2 :
Open the registry and go to:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters
Set the two variables:
EnableHttp2Tls and
EnableHttp2Cleartext to 0.
(If they don't exist, create them; they are DWORD32).

Effect:
EnableHttp2Tls = 0 disables HTTP/2 on secure connections (HTTPS)
EnableHttp2Cleartext = 0 disables HTTP/2 on unsecured connections (HTTP)
HTTP/1.1 will be used instead.
This protocol is slightly less efficient than HTTP/2, but the difference will not be noticeable.

I just tested it on Steam Cloud, and the save is almost instantaneous, as it should be if HTTP/2 wasn't broken.

Hope this can help.