2019 IMAC Desktop I purchased a used Mac desktop. All my purchase info is in the Mac which is seeking a BIOS number.

I'm not sure what a "bios number " is in Mac terms. Can you post a screenshot or a picture from a phone?

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Did you buy from a school or company that used managed computers? If so, only the school's or company's IT department can clear/unlock that. It's another level of security/anti-theft protection the some organizations use. Oftern a screenshot of the log-in request gives a clue.

.... its been almost two years.

So I guess that a refund is beyond all hope?

What do you mean it wants a "bios number'?

If you mean it's asking for a firmware password, you'll have to ask whoever you got it from.

There is no way to bypass that unless you are the original purchaser of the device and still have the original proof of purchase, which you don't.

(it looks like this)

If that's the case and you can't get the information from the seller, it is officially a boat anchor. There is not way past that and no way to recover any data that is on the device.

Servant of Cats wrote:

But if the previous owner had set a firmware password, the Mac would have demanded the password every time that it was powered on. I am unaware of any scenario where you could buy a Mac with a firmware password that you don't know, and put any data on it, or use it in any way, before being locked out.

A Firmware Password demand will only appear in the three specific circumstances described in Set a firmware password on your Mac - Apple Support. It is entirely possible to use a Mac for a very long time before finally encountering it.

"I was using it for a while and then I had to update it ."

There you go.

A longstanding contributor to this site whose opinions I respect has stated "never buy a used Mac". I am beginning to lean in that direction myself.

John Galt wrote:

Servant of Cats wrote:

But if the previous owner had set a firmware password, the Mac would have demanded the password every time that it was powered on. I am unaware of any scenario where you could buy a Mac with a firmware password that you don't know, and put any data on it, or use it in any way, before being locked out.

A Firmware Password demand will only appear in the three specific circumstances described in Set a firmware password on your Mac - Apple Support. It is entirely possible to use a Mac for a very long time before finally encountering it.

My bad. I had assumed that the firmware password prompt would appear all of the time.

The OP tells us that "I was using it for a while and then I had to update it … I just want to get my info".

But if the previous owner had set a firmware password, the Mac would have demanded the password every time that it was powered on. I am unaware of any scenario where you could buy a Mac with a firmware password that you don't know, and put any data on it, or use it in any way, before being locked out.

Perhaps the OP would like to explain further?!?

Re: “… I had assumed that the firmware password prompt would appear all of the time …”

One of the reasons they can be so “dangerous” to unsophisticated (or simply poorly organized) Mac users.

Since they are only rarely entered … it’s easily forgotten … and too few users keep an accurate and a “readily accessible years later” list of these sorts of minutia.