Sub domained multysite with one database

Just remove the empty sub-domain folder.

When you use any sort of WP, it works by receiving server requests which do not match any specific server resource. Any time a resource actually exists, WP does not receive the request. When you use sub-domains, WP rewrites them into a normal sub-folder request. That sub-folder must not exist on the server or WP will never see the rewritten request.

I think just #1 is enough, since you’ve already done #s 2-4 once. It should still be valid once the sub-folder is gone. If that fails by itself, try #3. #s 2 & 4 would be the same no matter what is done with other sites.

Sorry, no. All correspondence with me must remain in these public forums. Lets review what you should have done.
1. Started with a single site installation where pretty permalinks work correctly.
2. Add define( 'WP_ALLOW_MULTISITE', true ); to wp-config.php
3. Do the “Create a Network” tool. You should have chosen a sub-domain network.
4. On the resulting “Enable a Network” screen, copy/paste the offered code to .htaccess and wp-config.php as directed.
5. In your hosting cPanel, add a sub-domain and direct sub-domain requests to the root WP installation. NOT a sub-folder.
6. In WP network admin, add a site using the same sub-domain.

The above is covered in more detail at https://ww.wp.xz.cn/support/article/create-a-network/
but it’s light on what to do on the hosting side because what to do varies by host.

If you can provide a link to your sub-domain site, I can see if any clues are evident from the outside. What I can see is limited, but something might stand out.

Sorry, no. I will not access anyone’s dashboard. You shouldn’t offer privileged access to complete strangers on the Internet. That is very risky behavior. I appreciate you trusting me, and I certainly mean no harm, but I could still accidentally do something stupid and screw up your site. I don’t want such liability. Please delete that account or change it’s password. While I removed it here, by now it’s been scraped hundreds of times and can be found by anyone caring enough to dig for it.

When I said I would take a look from the outside, I meant as a random visitor to the front end. I can watch my browser’s requests and your server’s responses and maybe get a clue to what’s going on. It’s not much, but a clue might present itself. In any case, I don’t know your site’s URL, so I can’t look at anything as things stand.