Prem TV shows most, but the quality is garbage and there’s no app, it has to be done via a web browser. The price is decent, think it’s £5 for a game, or £90 for the season for all games.
As mentioned TNT sports show a fair amount of games and also in UHD, but that’s more expensive.
If you have a relative/friend in Australia, Stan sports show quite a bit, which you could watch via a VPN but I guess it’s not strictly legal.
If it is Rugby League you watch, ignore the above.
The game of Union has an uncertain future. Lot of small local clubs simply giving up due to bizarre tackling rules. The RFU won’t allow certain clubs to promote to the Premiership due to stand sizes but those clubs won’t ever be able to afford bigger venues without being in the Premiership. There’s also a lot of dodgy money going on, the game really isn’t in a good place at the moment.