The general rule presently is, where appointments are hard to get and leads to a made appointment that is after a deadline, the date that the (online) appointment was made is considered to be the date of the application under the condition that you attend that appointment.
A copy/printout of the appointment is advised.
For the extension of a residence permit (when the residence permit has not yet expired) this means that the date that the appointment was made is the date of the application for extension, then the residence permit is considered to have been extended until a decision has been made (§81(4) - Applying for the residence title - AufthG).
It is my impression that it is legal to leave the Schengen
zone Area (specifically Germany) with an expired work/residence permit, then almost immediately re-enter with a passport which grants 90-day Tourist visas stay -- right? If so, would it then be illegal to continue working while in Germany on the Tourist visa?
If you have made application/appointment for the extension of a residence permit while residence permit was valid
- then the residence permit has not expired
- you can continue working until a decision has been made
- there is no need to leave and reenter the Schengen Area
If you have not made application/appointment for the extension of a residence permit while residence permit was valid
- then the residence permit has has expired
- you cannot continue working
The potential trouble is only with leaving and re-entering.
A copy/printout of the appointment (or a Fiktionsbescheinigung) together with the residence permit card will be helpful in this case. Take into account that a possible verification of the appointment may be time consuming.
Update: based on the text of the Immigration Office Berlin FAQ Booking an appointment, you should not travel without getting a Fiktionsbescheinigung beforehand.
Landesamt für Einwanderung FAQ Booking an appointment:
My residence title will expire before my appointment. Is that a problem?
- Moreover, you can travel abroad only within the scope of validity of the residence title most recently granted to you.
I would like to travel but my temporary residence permit expired or expires very soon. What can I do?
If there are no available appointments before your travel and you are in possession of a valid travel document (passport or an equivalent), please send an email including your travel dates and the reason for your travel to the unit responsible for you. We will process your request promptly and check if you can receive a certificate that enables you to travel [Fiktionsbescheinigung].