Is the wet/dry mix you are referring to the overall program mix, the individual algorithm mix, or the insert mix? I think you’re referring to the insert mix, but I wanted to be sure.
The H90 automatically switches the algorithms’ input and output modes between mono and stereo according to what’s connected to them (by detecting which jacks are plugged in and what’s upstream or downstream of them in the routing). Bypassing/activating an insert won’t change the mono/stereo settings.
In the case of stereo output with a mono insert last in the chain, the algorithm just upstream of the insert will have its output set to mono, regardless of whether the insert is bypassed or not, or what the insert mix setting is.
Having an indicator for stereo or mono mode is a nice idea.