I use the built-in screen sharing to access a 2014 Mini media server and 2012 Mini file server from my 2018 Mini. The 2012 Mini is "headless" so it has a dummy HDMI plug which makes it work better with screen sharing. These machines are all on my gigabit ethernet LAN and there is some latency when accessing the other Macs. If I play a movie on the media server, for example, the resolution is reduced when it starts and some frames may drop as it plays. Screen sharing doesn't support audio, which might be a problem if the other Mini isn't in the same room with a speaker connected.
Really depends on what you're using the new Mini for. It wouldn't be a good solution for video editing, for example