Users can also interact with the smart contracts directly without the front end. Those smart contracts are also immutable because the ownership has been renounced.
Yes, the problem is that some of these are already being blocked on the RPC level. So if you use Infura or Alchemy (which are the default on Metamask), you can't interact with the smart contract. You would need to find a free RPC or run your own.
Also, it has begun. Blocking addresses is expected from centralized exchanges, however, a Defi exchange is also blocking addresses that connects to Tornado Cash hehehe. This is head shaking. They might be very afraid of being arrested and given a lawsuit for moneylaundering.
There is also an open source browser extension that intercepts and bypasses the requests responsible for checking if your address is dirty/sanctioned:
https://github.com/qd-qd/pineapple