Maybe this could be of help. This does not cover all games producers, but still...

Playngo: up to 6 RTP Variants between 99% – 84%
Pragmatic Play: almost all games up to 5 RTP Variants between 96% – 87%.
Red Tiger: almost all games up to 5 RTP Variants between 98% – 90%
Nolimit City: almost all games 2 RTP Variants: 96% & 94%
Spinomenal: almost all games 4 RTP Variants 96% – 89%
Habanero: almost all games up to 4 RTP Variants between 98% – 92%
Swintt: almost all games 2 RTP Variants: 95% – 92%
isoftBet: almost all games 2 RTP Variants: 96% & 92%
Push Gaming: several games 2 RTP Variants: 96% & 95%
Netent: many games up to 8 RTP Variants between 99% – 90%
Microgaming: several games 3 RTP Variants: 96% – 92%
Blueprint: a few games 2 RTP Variants: 96% & 94%
Quickspin: a few Games 3 RTP Variants between 96% – 90%
Thunderkick:  One game 2 RTP Variants: 96% & % 94%
ELK: Can't be adjusted
Yggdrasil: Can't be adjusted