I’ve read many results that come from https://www.notebookcheck.net/ , which often even has detail on even the usually too-boring-to-review business cheaptops I often have to purchase.
I find it to be a resource to a often a very good level of detail, but if you want to be certain before clicking buy you want the field service handbook for the laptop before final consideration, if those questions are critical. If the manufacturer doesn’t feel that’s important, it’s probably bad news.
Sadly there isn’t a master list, it’s kinda a mixed bag honestly. I usually hit up ifixit to see if someone posted a guide on a given laptop, but if its a relatively new machine, you’re usually better off seeing if you can get a pdf directly from the manufacturer.
That being said, even the manufacturer is rather vague at times of what is coming in each machine and what the upgradability is. I’ve had excellent luck with Dell, HP, ASUS, MSI to have support documents available that show most upgradeability. Dell’s service tag system is excellent for checking what the system came with.