Author affiliation for co-authors not currently affiliated with an academic institute
Listing a former affiliation as if it is current is not right. Listing an employer as an affiliation may run afoul of their rules. Permission may be required. And if they didn't support the research it is good for disambiguation purposes but no other.
Listing yourself as an Independent Researcher is correct in almost all cases, though your employer should probably be consulted as there may be contract obligations.
No affiliation is fine if the journal (or whatever) permits it, but for people with common names is less than ideal. But don't worry that it stands out. People rarely care much about it unless they want to contact you.
If you have an established personal &quot;business&quot; perhaps for tax purposes to manage income from publishing books and such, as I do, then you could list that. It is accurate and honest. But it might need to be public enough to enable people to use it to find you. And, creating a bespoke organization for this purpose, especially as a one-off, doesn't really help for any of the usual purposes.
But affiliation in general is used for several things. The most important is probably to indicate support from an organization, though disambiguation of names is also quite important. And a previous affiliation treated as if it were current could be interpreted as dishonest. And if someone tries to contact you through a previous affiliation and is told that you are in no way affiliated with them then you could suffer a bit.
However, specifying &quot;Formerly a student at Universal University of the Universe&quot; is fine, since you are clear about the intent.

And a warning. Some employers require you to get permission to publish most everything. Some will forbid publication if it affects their core business in any way. Know what is in your contract.