Nevada did approve server-based slots back in 2008. I don't know how many casinos actually are using them, however. Additionally, they could be using them to manage some banks of machines, while leaving other machines in a traditional configuration.
In Nevada, a machine must be idle for at least four minutes (no play, and no credits on the meter) before any remote changes can be made. In addition, if a change is being made, the machine will be placed out of service and a message on the screen will indicate that the software is being changed. As such, casinos aren't changing machines on the fly because "John Doe" put in his player's club card and they want to really tighten the screws on him today. However, they might use the technology to change a bank of machines from penny denomination on a weekday to a nickel game on a weekend, or something like that.
Other jurisdictions do not have to follow Nevada's rules, and as such could be more or less restrictive as to the use of the technology.
Note that while long-term payback percentage
could be altered in a server-based setup, it cannot be used to force a machine to payout a jackpot on a holiday weekend, or withhold a jackpot on a certain day or time period, or anything like that. Yes, they could change a machine from a 95% payout to an 85% payout, but that doesn't significantly change the odds of hitting a jackpot, and anything can happen in the short term.
Here's some reading from years ago about the technology:
https://lasvegassun.com/news/2008/feb/17/dont-worry-your-slot-bets-are-still-safe/https://www.lasvegasadvisor.com/question/2008-07-09/In this 2022 article, Las Vegas Advisor says that server-based systems "never caught on with the casinos." That may be true for Nevada, but I've read that they are popular in other jurisdictions around the world.
https://www.lasvegasadvisor.com/question/changing-slot-payouts-on-demand/