This nonsense that you are claiming that every folder in windows has always had a read only attribute attached to it for the files inside is preposterous and categorically false.
I've never made such a claim. What I've stated is that the "Read-only" checkbox in the folder properties dialog will look the same for every folder. That is, it will be a solid black box on Windows 10 or a solid blue box with a horizontal line on Windows 11. Go take a look at the properties of any folder on your computer. That checkbox will look the same on all of them.
We have all been conditioned to expect that a checkbox gives us some useful information. This is a case where it does not. That checkbox is just a control that will let you set all files within the folder to read-only or clear the read-only attribute from all files in the folder. Try that on a test folder and then close and re-open the folder properties. Whether every file in the folder is read-only or none of the files in the folder are read-only, that checkbox will look the same.
And even if it was true a read only attribute would never be meaningless, seeing as the main reason for the possession of any computer for the vast majority of people is so the they can create and write new changes to files.
Also, as I've stated many times, that checkbox does not change the read-only attribute of the folder. It's only used to change the read-only attributes of files within the folder (and it states that right there on the screen).
But let's pretend for a moment that your folder's attribute was changed to read-only. Would that prevent creating, deleting, or changing a file within the folder? No, not at all. A folder's read-only attribute does almost nothing. To prove that to yourself, create a folder and use the attrib command to set its read-only attribute (e.g. attrib +r c:\test). Then try to create, delete, or change files in that folder. You will find that you still have full access. You can even delete the folder itself in Explorer without a warning. The only difference you will see is an error if you try to delete the folder at the command line.
A truly read-only folder is one where your effective permissions only allow read access. That can be a situation where the NTFS permissions are set to restrict access or a situation where a network share is set to read-only. You didn't mention a network, so I'll assume we're talking about a local drive in your case. If you check the Security tab for your folder and find that somehow the NTFS permissions have been changed so that you now have effectively read-only access, that's obviously a serious problem, but it has absolutely nothing to do with the "Read-only" checkbox that you see under the "General" tab.
Microsoft support themselves could not fix it last night while taking control of my PC.
No surprise there. I suggest taking advantage of one of the many enthusiast online forums, such elevenforum.com. Present your problem there with screenshots. You may find that someone there has already been in the same situation and knows the answer. Or maybe not. There's no guarantee, but it's worth a shot. Reddit can also be a good place to present such issues.
YOU are the one barking up the wrong tree by spreading misinformation as a generalized truth.
The only misinformation has come from misunderstanding what I've written. I have provided facts to try to prevent people from wasting their time looking at something that is irrelevant to their issue. If you wish to prove that I have made an error, please quote my actual statements and provide proof, in the form of screenshots, that show I've made an error. I am happy to admit my mistakes when I make them. I am not perfect, but I'm sure I have made correct statements in regards to this issue.