Make blocks unbreakable via config. Simply add whichever block you want to not be breakable in the form of modname:block_name inside config/bedrockblocks/disabled_blocks.json To make certain players bypass this restriction, simply add them to the whitelist inside config/bedrockblocks/whitelisted_players.json After changing the configs, either restart the game, or run the reloadbedrockblocks command.
This is mostly useful as a server-sided mod, to prevent players from breaking certain blocks. It only needs to be installed on the server.