What is your use case for trying to RBF txs that do not signal RBF?
~All txs created by Electrum signal RBF. Is it to bump the fee of txs created by other wallets?
Yes the idea to RBF a non-RBF transaction, ideally there is no way to turn an already non-RBF transaction to a RBF transaction, the way round that is finding a node that actually has its setting as Full RBF this kind of nodes will still accept double spending of same transaction with a bigger transaction fee and then remove the older transaction from its mempool. Using electrum is just to change server and actually look for that one with a Full RBF mempool setting. Not that it will automatically change the transaction to a RBF one