While it's impossible to track which blocks a player has broken, it would be easily possible (however intense on both server resources and admin's time) to enforce some simple protection. The only real things you could enforce with a reasonable amount of effort would be valuable blocks. Basically, you would give each player and id, and then when they break a "protected" block (a beacon, for example) a scoreboard detects it. An invisible, no-hitbox armor stand is summoned at their location to mark that it happened, and it is given a score based on the id of the breaker. When one of these armorstands exists and an admin is on, it sends them a notification and the coordinates. They can then pull up the table of player ids and figure out who broke it and then if it belonged to them.

Of course, if you were using spigot there would be far easier plugins to use. If you're on a realm or something though, this is the best you've got.

This is definitely something you'd want to solve with a plugin, not a datapack. The problem is that Minecraft doesn't know the concept of variables, and although you can easily store and retrieve single values it becomes quite a hassle if you need to start working with collections.

And there are already some very good solutions for this out there. GriefPrevention and CoreProtect come to mind here.