I do not recommend installing Windows 11 into any PC for gaming at this time, it has so many problems and performance issues and missing features from Win10. Win10 will have the most compatibility with modern games or whatever you choose to play on there. If you're going with ryzen, make sure to get fast ram, Ryzen processors like fast ram, so any sort of DDR4 3200mhz speed or above should be fine. DDR5 is in the early stages of being in the market and won't drop in price or is worth it in the meantime if you ever wanted that. I personally have a 2x8GB kit of Corsair LPX Vengeance ram rated for 3200mhz.
For the motherboard, refer to this VRM tier list on the LTT forums
https://linustechtips.com/topic/1137619-motherboard-vrm-tier-list-v2-currently-amd-only/ , reveal the contents of the AM4 list, and look at the ones that pertain to your Ryzen 9 processor of choice, anything from tier B or above should be good. Good VRMs are important for overclocking, but they are also important for powering your Ryzen 9 with boost clock speeds on by default PLUS powering your ram at 3200mhz or higher. I had a VRM problem when I chose to get a Gigabyte DS3H motherboard the first time which was pretty much down in the barrel in the list, it kept crashing due to power requirements for having the boost clock speeds and having the ram running at 3200mhz. I'm sure plenty, if not all those motherboards that would work great for your needs will have some RGB light accents on the board, so keep notes on every sort of part that will satisfy your computer power and RGB light requirements.
As for the case, it would be a good idea to get all the parts into a list on pcpartpicker so that any sort of case that may have built-in rgb lights is also able to fit everything inside. Either that or you can get rgb strips designed to be installed inside a computer case, onto the motherboard; gaming motherboards usually have an RGB header so you can install a strip of RGB lights or an RGB controller to install multiple strips of lights so that you may control them on your computer.