Issue them digital wallets to enable holding global reserve currencies. It is an AML/KYC problem. Imagine if, just for the sake of argument, any of these unbanked folks in countries you mentioned could install something like TransferWise (which app doesn’t matter, but the ability to tie your identity to your account holding various value stores) and hold whichever currency they wanted digitally. No stablecoin, CBDC, or blockchain required.