Just an opinion i think add Altcoin like ethereum litecoin or usdt can be choice to buy copper membership and donation since bitcoin have high fee right now
This is BitcoinTalk, not EthereumTalk or LitecoinTalk. I don't support adding alt currencies for donations or memberships.
And seeing that Ethereum has even higher fees than Bitcoin, adding ETH/USDT (an ERC-20 token) makes no sense.
If you don't wanna pay $5-$10 in fees you could wait for the weekend and make the purchase then. Right at this moment, you would be paying 26 sat/vB for a high priority transaction, which if your transaction has only one input comes out to about $1.74. I wouldn't call that expensive.
Although I feel it would be beneficial in the long run to add support for Lightning network, seeing as how SMF works (and runs on PHP), I don't think it would be a trivial task to integrate LN here.