I've used Startech FTDI based multi-port serial to USB adapters along with a Mikrotik Routerboard to make serial-to-ethernet or serial-to-LTE boxes. The Mikrotik boxes expose the serial port on a TCP port for you to connect to.
Old multi-port serial consoles can often be found used quite cheap.
Personally, I'm a big fan of the OpenGear units. They're *much^ more than just basic serial consoles and are quite extendable. You can even write your own scripts to interact with them, trigger them on specific events, and so on.
If you have better recommendations feel free to share them :)
[1] https://freetserv.github.io/ [2] https://www.pcengines.ch/apu2c2.htm [3] https://www.delock.de/produkte/G_95244/merkmale.html