Yes, that would mean you should amend 2023, then include the installment, Form 6252 in each year you receive proceeds.
Optional. If you did use your full cost basis in 2023, then you can report the amount received in 2024 as a capital gain by using zero cost basis. This taxes the gain (full amount received) in each future year. You would have to enter a sale date of 2024, 2025, etc.
Since the stock was from a private company (not publicly traded), then you might consider using option 1 or 2 provided by Mike9241.
@evelyn-chambers
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