You can compare data sheets for details, but basically the "Room Kit" series are the newer technology. they will support higher resolutions for presentations, have the power for some AI features, etc.
The SX80 is effectively being replaced by the "Room Kit Pro", which has similar numbers of I/O ports. The Room Kit Plus doesn't have as many I/O ports. If you're buying a new system I would recommend going with the Room Kit option that makes the most sense for you, the SX80 will likely go end of sale this year.