David Haveman

I am having the same issue.  I logged out and logged back into the mojang account.  The launcher ignored the "launcher_profiles.json" file and only cares about the "launcher_accounts.json" file now.

this aspect of launcher_profile doesn't even change when i restart the launcher ( like it used to )

"profiles" : {
        "fake-profile-key" : {
          "displayName" : "Daddy"
        }
      },

I have the same launcher version and am also on Windows 10.

I am only trying to connect to a local server in my own network.   

I get this issue as well when trying trying to connect from Windows 10 clients with Java Edition 1.16.2, no mods, vanilla server/client.

it differs, but it is all kinds of bad packet, wrong number of bytes received, etc.