I made a video about one of them, Megaways Gold I think it was, it was on my old YT channel but I've never reuploaded it to my new channel.
From memory I got it up to over 300,000 Megaways in the bonus for multiple spins, but it can do one million Megaways or something, and you can see the reels extended out in the game, at which point it becomes very obvious how they're designed to miss stuff all the time.
The most blatant one is alternating symbols, so reels 1 and 3 will be heavy with certain symbols, but reel 2 will have practically none of them, but then other symbols will be heavy on 2 and 4, but missing on 1, that sort of thing. So on Bonanza when you think you've 'just missed' a diamond or whatever to connect a big win, the reel that missed might have one diamond on it and be god knows how many symbols long. (
BTG games have famously long reel strips.)
They do it with the premium symbols as well, so you'll get loads of enticing looking premium symbols on a number of the reels, even stacks of them, but when the reels are extended out a long way, you can really see how they are almost completely missing from a critical reel that means you almost never get them participating in a win.
There was a thread here a few years ago doing a statistical analysis of the BTG game Danger High Voltage, that isn't a Megaways game but the same design principles held true, with really long reel strips and symbol distribution designed to keep the game in check - because at the end of the day all these things are running with a house edge of around 4% (or often a lot more these days), and without that symbol distribution you'd end up with a game paying 150% or whatever.
If you can find Gold Megaways on demo play somewhere, just lump away at it until you get a bonus that properly gets going on the insane number of Megaways, and watch how something like 330,000 Megaways either misses completely for multiple spins, or manages a 3OAK on fucking 9s or something.
I had a proper extended play around loads of BTG games a few years ago, and documented it here at CM in the appropriate threads, the conclusion I reached at the end of my endeavours was never to play BTG slots again
There's nothing 'wrong' with them as such, their 96% games pay out 96% over time, they don't cheat, they're not rigged or compensated, but once you get your head around how their game design and maths models work, they can become quite unpalatable.