Welcome to the openHAB forum! What you want to do should be pretty straightforward.
First, you need to configure the pico keypads on your RA2 Select hub using ipbridge rather than leapbridge, because the LEAP protocol (at least as far as our current understanding of it goes) doesn’t support key-press notifications. If you’re already using ipbridge you should be good to go. If you’re using leapbridge, I would recommend just configuring your keypads using ipbridge rather than trying to move all of your devices over. See the docs for an explanation of configuring ipbridge.
Next you’ll need to configure pico things for your keypads, and link some items to the channels for whatever buttons you want to use on them (if you haven’t already).
Finally, you’ll need to create rules that look for updates to those button items and take some action.
Here is part of a rule file (in Rules DSL) that looks for Pico button presses and sends commands to TP-Link dimmable bulbs based on them. Sending a command to a Shelly device should be similar.
val Number preset = 40
Item LibraryLightPico_Button1 received update ON
Item LibraryLightPico_Button2 received update ON
Item LibraryLightPico_Button3 received update ON