Correct, it's in my iframe and it works when my page is not embedded in itch.io. Meta tags are not inherited through iframes. So yes, even if the meta tag is in my iframe, it doesn't solve the issue.
You can easily check that adding the meta to the itch.io game page solves the issues. If you don't have any game page with an html game with an appearing keyboard I can privately give you the password to my restricted project.