BandCheck is a really simple network bandwidth check tool, working on Linux, macOS and Windows.
Run the same BandCheck.exe on one of the endpoint (a server, a client or other), to put it in listen mode, then run BandCheck.exe on another endpoint on the same network to test the available bandwidth.
On the first endpoint
BandCheck.exe -s
On the second endpoint (replace IPV4 address with first endpoint address or name if resolved)
BandCheck.exe -t 192.168.1.1