I would add that I've not heard of any foreigner being issued a new entry visa who doesn't already have a Residence Permit or similar visa and is clearly able to prove to their local Foreign Affairs Office that they are critically needed back in their job or otherwise critically need to get home so China is completely out of bounds for casual visitors at the moment.

Not only is each city dealing with returnees differently as noted above but each local Foreign Affairs Office will have its own process for issuing Invitation Letters that are now required to get new entry visas issued in addition to an Invitation Letter from whoever it is that's actually inviting you (most likely your employer) and these rules and processes are fluid.

I'm happy to offer advice to anyone aiming for Shenzhen if you message me as I'm currently in the process myself.