I have zero experience with this problem and I’m just spitballing but I’d consider. (Note that I’m rather stupid, don’t own a home, and uneducated about electrician stuff):

• Some kind of epoxy to just totally coat the outside. Slather it on and it hardens and I don’t have to think about it
• build a little enclosure around that bit so it’s living a bit more “inside”. probably impractical but a fun challenge
• wrap electrical tape, then pipe insulation. Tape over the pipe insulation then brush on something that cures into a waterproof seal

Also ask an electrician