If I don't want a first.last@domain.com type of email address, and instead opting for a verycommonfirst[2-9]@domain.com, e.g. jack2778@something.com. Then, having a GitHub username resembling the same pattern jack5588 and also copyright noticing my work by it like so:
"Copyright 2020-2021 jack5588"
jack2278@something.com (or maybe jack@someremailer.com) will be also my contact email listed on GitHub for the purposes of "proof of ownership".
Will this go down well or is it a stupid idea making a potential employer/interviewer raise eyebrows?
There's another way to pull this off, but I don't want to go by a hash: https://opensource.stackexchange.com/questions/7147/declaring-copyright-anonymously
My intention is having some simple privacy by not being easily searchable/identifiable via a search machine. I intend to use my very common real first name though.
Note, the [2-9] is because 0 and 1 can be hard to correctly read out.
PS: I know Linus Torvalds won't let me contribute to his projects at all, if I choose to do that...
You're overthinking it. Unless your email name is "IStealFromMyEmployer@example.com", no interviewer is likely to pay the slightest attention to what your email name or GitHub account name is. (Most of the time, they won't even look at your GitHub even if you mention it on your resume.)
Attempting to copyright your work under a pseudonym may have legal implications; you may wish to investigate that if you think your code will eventually be of value.