Crikey! cool down peeps, it's a pretty basic, straightforward and resolvable point!
Right, Relax Gaming (who
BTG still use as their platform) certainly do offer variable RTPs for their games, but not as low in range as Netent/PNG. They just tend to be a 50% higher house edge variant (which means 94% player RTP as opposed to the factory 96%) and that's true of Pragmatic Play and NLC and Push Gaming as well. So this applies to Relax and any smaller developers they have that actually do this. Then consider
Relax are now part of WMS-SG-Light & Wonder who also have numerous developer names within their fold of which many offer variants too. BTG as far as I am aware from the game sheets that I have seen still don't offer lower versions although I think it's only a matter of time.
EDIT - P.S. Yes, there are clearly different versions of Bonanza (we know this anyway from the 'version code' in the game files) but they all have the same RTP. Why this is, I cannot say for sure but I'd suggest that being the main bed of Megaways feedback Bonanza would be ideal to 'tinker' with, not necessarily at the behest of the casino or platform but the developer. If you remember, one of the earlier observations about the game was the fact you couldn't get max ways in the bonus, which was changed for WWTBAM and other BTG Megaways since, including the most recent Max Megaways slot. We know the version SkyVegas and some other casinos used would never produce scatters in max ways spins for example, therefore giving more likelihood of bigger wins in their place.
As for NYX, they don't exist as such any more. NYX Open Group began in 1999 and were primarily a platform for Nextgen Gaming slots and others too, but are now owned by SG Digital/Light & Wonder as are Relax. So it's likely that if they haven't already, you'll be seeing a single platform not the both.