I created a button in my toolbar for this reason. It toggles all envelopes hide/show using a single Reaper action "Toggle show all envelopes for all tracks".
It hides/shows ALL envelopes at once but since it's a single click it's fast and easy to toggle hide/show.
CAUTION HERE: When you hide envelopes in Reaper using this action they become DISARMED and go into "Trim/Read" mode even when set to "READ". In Trim/Read mode you can move controls independent of the automation data - which makes it appear automation is not doing anything when in fact it is.
I don't like that functionality SO I also turned on the settings highlighted in yellow below to make sure faders and controls always MOVE when in READ automation mode even when envelopes are hidden. The "Allow writing automation" box is misleading - what it actually does is keep the envelopes ARMed which is required for controls to move in READ mode. Be careful when automation is set to any of the "write" modes with this box checked!