Can someone help me understand if there's anything I can do to increase the number of options I get on the mobile client(s) where I can choose to live transcode to reduce the data rate?

The context is that I have a number of 4k films with high bitrates (>100Mbps) which work fine over the wired connections in my house. But if I want to stream them over my WiFi, it isn't supported (I only have 1Gbps WiFi throughout and we all know that that's just a theoretical limit). I therefore accept that I need to turn the quality down but I have no options above 1080p.

Is there no way of turning the quality down to reduce the bitrate without turning the resolution down to 1080p?

If I buy a Plex pass, do I get more options?