It has been turned on by default for quite some time, since one of the version from 2018.
Electrum has supported RBF some years ago, but if RBF is enabled, you will need to still flag the transaction to support RBF, unlike now which is dafault while sending unless you flagged the transaction not to support RBF.
No offence, the post is actually extremely wordy and some better structuring would be needed.
I tried my best to reduce the post contents, but will result to missing of important information for newbies. Just trying to simplify it as it could be.