How can I protect private items in chests in vanilla Minecraft 1.12?
I too have a realm and what you could possibly do is turn keepinventory on if It isn’t already and just give players loads of skulker boxes which they can use to store items instead of placed chests. Sadly, i can’t find a way to make chests invincible and locked without plugins or mods so this might be the way to go. Sorry if this wasn’t the answer you were looking for.