MetaMask only works for EVM-compatible transactions. For native EEL wallets, use the wallet and converter pages to derive addresses locally.
RPC should be proxied through nginx and backed by 127.0.0.1:8080. Do not point MetaMask directly at public backend ports if nginx is already in front.
If the chain is not EVM at the protocol level, MetaMask can still store the network, but signing native transactions will not work.