Hi Fireman26 , if it only has a registration number, then the next step is to call MYOB and discuss how to upgrade.
Prior to the introduction of serial numbers, it was possible to use MYOB programs unlicensed, ie without paying for them.
The equivalent software right now is AccountRIght Premier, desktop version. (Browser versions exist but are not as fully featured).
I suggest you discuss the plan with your supervisor, that is you plan to call MYOB, give them your registration number and company name, and ask their advice about upgrading. They will send you a quotation, note that today's programs all require a subscription. Obtain approval before taking any action.
The program might work on Windows 11, but you should really not be using such an old program.