I actually have a lot of experience with this one! Back when it was Marvel Jackpots (the same system, just rebranded due to Marvel not renewing their sponsorship), I used to gamble a lot. I’m talking £12.50/£25/£50/£100 spins (funded from a large win prior). I actually triggered the random jackpot feature about five or six times. It was honestly the most exciting thing, as it would happen randomly at the end of the spin and was incredibly tough to get. I made it a lot easier due to the frankly insane stakes I was making, as this increases the odds of it appearing.
5 of the 6 was just the Power Jackpot which was around £130ish a time, but one of them I managed the Super Power Jackpot for £25k. Was absolutely buzzing!
Most casinos do count jackpots separately from bonus money, as they are funded by the provider and not the casino itself (except for local jackpot slots). T&Cs vary from casino to casino. In my case, it was bonus money unfortunately, but I managed to wager it successfully after a few hours of high stakes play!