I think the closest to what you're looking for is this:
Activate your phone, device or AT&T Prepaid SIM card purchased from Walmart, Target, drug, grocery or discount stores.
www.att.com
Yes you need a SIM but it needs to be a new unactivated SIM which only costs a few dollars. These should work
https://www.amazon.com/gp/product/B07P2GPYQ5/?tag=rvf01-20 which are 2 for $6.85. I think they're even cheaper at Walmart etc. The ICCID has to start with 890141 which means it's AT&T prepaid.
Here's a valid SIM ICCID that you're welcome to try for the purpose of submitting the first step on that form. 89014104272133835673
Enter that number, your IMEI and zip code and see if you can get to the next page. It does some sort if IMEI compatibility check when you submit that first form because I've seen it return with an "Incompatible IMEI" message. My guess as that if it accepts the IMEI and gives you a choice of plans on the next page then it will probably work. In that case, you'll need to get your own SIM and start again. Don't signup with mine. I think I've lost that SIM so I don't feel any risk publishing it here. At that point you really need to risk $35 for 15GB or $55 for 100GB to see if it really does work. No guarantees on anything I'm saying here.

I don't know if "passes the first form and probably works" means that it's "certified".
I find the att.com site to be totally confusing and generally a challenge to use. If you look for data only plans you end up here:
Check out our new data plans for prepaid mobile hotspots and tablets. Connect to the Internet with more data now with 5G access, new flexible pricing and no credit check.
www.att.com
That page has basic web user interface problems. If you scroll down to "Get started" and then "Have your own device", the "Activate it online" text with a right pointing arrow is not clickable. You need to click the title or the image.
As far as I can see, that $55 for 100GB is the best plan a non-business customer can get from AT&T. Of course 100GB is not really enough for many people.