It sounds more like a hobby than a business.
Why would you want to draw attention to it by filing an S-election now, hoping to make it retroactive?
Why does the company want to be an S-corporation?
It's going to cost them a bundle to have you do their past bookkeeping, payroll, financial statements, personal returns, etc. I hope you have a huge retainer. Can they afford you? Can they afford all the P&I?
If they came to me and insisted on a much-too-late S-election, I'd send them elsewhere!
If they came to me to make a fresh start, I'd work with them to treat their casual hobby/business like a real business. I would not rewrite their history.
Depending on their income and long-term plans (do they want to take in a new shareholder, for instance?) I might suggest an S-election for 2023, after I've seen them make the changes I'd require.
If you have time to redo 2022, you might make a late election for 2022.