If your iPad must be restored because it cannot boot, it has to be connected to an external computer so as to reinstall the Operating System. As frustrating as this sounds, there is currently no other technical way to do so.
Look at this logically:
- Your iPad will not boot.
- Your iPad will not correctly respond to the few hardware buttons with which you can interact with it.
Other than connecting to a PC/Mac, given that all the Apple Stores are closed, the only other course of action available to you Is to directly contact Apple support. I fear however, that they’ll not be able to offer more than we have already tried and outlined - but at this point, what have you to loose in trying?
I’m sorry that we’ve exhausted the available options without achieving a fix. I sincerely hope that Apple Support might be able to offer an alternative.
The Contact Support link is at top-right of this page. Please do let us know how your get on. If a solution is identified, it could help others that find themselves in a similar situation.