Work with automation.
I set track mode to touch.
To be sure I go to preferences: Hidden envelopes: Allow writing automation.
I arm volume envelope and dont want to see it so make it not visible.
I try to write automation to hidden envelope (armed).
Result:
There is none automation data.
Basically when I unticked visible checkbox arm checkbox was unticked too i believe but graphic did not update in envelopes window.
Writing into unvisible envelopes is important as messy tons of envelope panels for every automated parameter visible and clicking thousend times to hide, arm, activate for every envelope for each track as we cant select multiple envelopes across tracks and even on same track, and zooming and scroling is causing chaos IMO.
@edit
So topic should be even: Reaper says u can write automation to hidden envelope but u dont.
I tested more and seems like u can write in write mode but no in other types of write mode like touch and latch.