I get this from one of my Linux boxes that is ethernet attached - this is a 2011 MacMini running Debian. As you can see the speed returned is pretty much as fast as you're going to get with the technology.
https://i.imgur.com/VPm3FaT.png
That test server is definitely capable and every time I run tests against it at any time of day, its full speed.
You might need to check what else going on your LAN at the time you're doing the tests. If nothing and you're still not getting max speed, something locally can't keep up.
Edited by nofappingway (Fri 14-May-21 13:59:49)