There are several websites that offer GBA ROMs for download. Here are a few popular ones:
Most people use a Megathread to load games onto a (like the Everdrive GBA or EZ-Flash Omega) or a handheld emulator (Anbernic, Miyoo Mini, Retroid Pocket). gba roms megathread
The Megathread solves the : Physical media rots (bit rot, battery failure, cart oxidation). Digital storefronts close (RIP Wii U and 3DS eShops). The only entity currently archiving the complete GBA library—including bootlegs, regional variants, and prototype dumps—is the shadowy collective of anonymous ROM preservers. There are several websites that offer GBA ROMs for download
The "megathread" format is preferred because it aggregates information across emulators (mGBA, VisualBoyAdvance-M), flash carts (EverDrive, EZ-Flash Omega), and mobile solutions (Delta, RetroArch). flash carts (EverDrive