Re: genesis bday present

If you are looking for region free support, the later revisions of the Mega Everdrive have a feature called "MegaKey" that can offer region-free game loading for certain titles, as well as the ability to use Game Genie codes that can also bypass region locks on certain games. How region locking worked (and whether it existed) differed by title on the Genesis, and without a region switch mod to allow you to change the signals coming from the BIOS (which does require soldering) you might not be able to play every regional variant, although I do not know which if any titles actually require this mod.

What you're thinking of is called a flash cart, and yes, those exist for the Genesis. The "Mega EverDrive" series by KRIKzz is probably the most popular choice among enthusiasts, although there are plenty of cheaper generic flash carts on places like Amazon and Ali Express.