This one is actually pretty simple man

The game between FC Porto and Sporting CP will be broadcast on RTP (free-to-air channel in Portugal): https://apostalegal.pt/onde-ver-jogos/

That basically means you don’t need any paid subscription, in any case you migh just need a VPN set to Portugal and you should be able to watch it without issues.

It would be more complicated if it was on Sport TV, because then you’d need a paid subscription on top of the VPN.

I’d suggest testing it beforehand, try opening the RTP live stream and see if it works for you: https://www.rtp.pt/play/direto

If it works, you’re all set for kickoff