I am pretty sure that the Russian government can block whatever news sources they see fit, which of course is anything that makes them look bad. Never underestimate the power of a dictatorship when it comes to suppressing information.
In addition, it seems well known over there that speaking out can end up with you being placed in a room with no windows for a undetermined period of time.
In fact they can't block everything as has been pointed out in various threads. Many Russians are using Telegram which is still functioning and the widespread use of VPNs has also been noted.
Russians are still freely communicating within this thread for instance.
Further, the most severe media crackdowns occured after the invasion so many Russians knew what was building up and now are well aware they are being shown extreme propaganda on state media.
Additionally, intelligence which had intercepted basic communications from Russian soldiers back to family and friends found them discussing fellow soldiers committing murder and rape, looting and the fact that moral was low. Which would mean increasing numbers have a clear idea of what is taking place in Ukraine.
That said, yes, many are afraid of speaking out.