The Neighbors page of the Local Status Page shows all of the neighbors of a given Meraki AP. Access this page on an online AP and check the to see if the offline repeater MAC address appears in the table. If it does, the offline repeater is active and within range of the online AP.
Of what I understand, it will not show metrics and percentage details ?
So you should be able to have an idea about the signal strength. I don't have local access to an AP in mesh mode atm, so I can't comment on what the Connection tab shows in that situation. There may be metrics shown there too.