Got a question about blocking a computer. On the MK router I have the computer use a static IP and in the firewall I can choose to drop all traffic for that computer. It works for everything except the messaging program Discord. As long as it is open it maintains a connection. HOW?

It sounds like you don't drop everything, but only new connections. Rules are processed in order from top to bottom, so if you'd have standard "accept established & related" before you drop rule, it would allow existing connections to survive.

Here are the 1st four rules. The rule to block the computer in question is rule No. 3 (counting from 0 - 3), which I put on Drop for Action when wishing to terminate all internet activity. So would I have to basically disable the first rule (as the other 2 are to permit VPN connectivity), then enable Drop for Rule 3, then re-enable Rules 1?

No. It's not exactly as I thought. The first one is not real rule, you can't disable it. But it shows that you have fasttrack enabled and I don't know if there's a way to close fasttracked connection. One way would be to permanently disable the whole thing, but it's useful, so it's not the best solution.

Edit: One thing you can try is blocking in raw table, but I'm still not sure if fasttrack bypasses that too or not.

Blocking in raw table? What is that?

IP->Firewall->Raw, it's similar to IP->Firewall->Filter. Just use prerouting chain instead of forward. But remember, maybe it won't work either.

No. It's not exactly as I thought. The first one is not real rule, you can't disable it. But it shows that you have fasttrack enabled and I don't know if there's a way to close fasttracked connection.

Could you use a script to knock down all the existing connections for that IP?

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hey, list your fill firewall rule set, for both ipv4 & ipv6.

what I'm wondering: you have fasttrack dummy rule, but not fast track itself..., view is incomplete
fasttrack will bypass most of ip processing for bigger part of packets of a connection, but on regular basis packets will be processed with full path (to refresh connection tracking stats)-> if it's blocked then, connection will be terminated.

also fasttrack will no bypass raw, as it's based on connection tracking, which is established after raw filtering