Getting into red dots on pistols can be overwhelming at first. You want to get the best dot, but then you have to worry about optic cuts and making sure you have selected the right cut to run the red dot.
Different footprints go with different optics and some cuts cannot use adapter plates or adapter plates are not available, there are going to be tons of scenarios if you want to dig deep.
This is an excellent guide to explaining not only all the mounting points but also patterns, screw sizes, and models that fit what cut. Tons of really good information.