Hello Luca
You’re absolutely right. Just like OSPF, things like route filtering and route summarization can only take place at border routers. For OSPF that means at ABRs and ASBRs. For IS-IS, that means L2 routers. The reason is that by definition, for link state protocols, routers within an area must have the same LSDB.
One solution to your issue is to simply not enable the routing protocol on a particular interface, as you mention in your post. That way, the subnet of that interface will not participate in the routing protocol, and it will not be included in any advertisements.
However, there is another option. You can filter out what routes are to be installed in the local routing table. That way the route will still exist in the LSDB, thus you maintain the requirement of having identical LSDBs between routers in the same area, while picking and choosing which of those routes will appear in the routing table.
For OSPF, this can be done using distribute-lists, and more details about that can be found here:
For IS-IS, the idea is almost identical. Take a look at this NetworkLessons note on the topic of IS-IS route filtering.
I hope this has been helpful!
Laz