How to overcome the 404 error?

Question

Browsers

Recently, some sites have ceased to open, what is it connected with and where to dig?
ERR_CONNECTION_TIMED_OUT error.
PS Tried all sorts of browsers, Windows rolled back, Windows Defender turned off the Firewall also turned off.

Answer 1

Did you ask Roskomnadzor?

Answer 2

https://isitblockedinrussia.com/ check against the lists.
https://downforeveryoneorjustme.com/ check resource availability.
In the case of blocking, a timeout occurs if the provider blocks the resource with a drop of all packets.

Answer 3

A proxy extension might be installed.