causing the engine no crank/no start behavior, the clutch interlock switch was very intermittent. It would not work then work and work and work and work, then not work.
If you don't want to take the car to a dealer where a tech can retrieve error codes (they are not OBD2 codes but are still read from the OBD2 port) then replace the clutch interlock switch and at the same time the brake light switch and the cruise control disable switches at both the clutch and brake pedal.
Once installed be sure the observe the clutch pedal lever properly contacts the interlock switch. With age the clutch pedal hardware develops play that can have the position off and the interlock switch is not quite pushed in far enough.
The switches are not expensive but it takes a contortionist to install them. At my dealer when I would buy switches, bulbs, the tech would install them for free.
There is a test of sorts... Get in the car and pump the clutch pedal vigorously then hold it down and start the engine. If the engine fires up turn it off and repeat. What one is looking for is to try to get the no crank/no start symptom to appear/not appear.
Another test, one for the ignition switch, is to do something similar with the ignition switch. With it off wiggle the key, push the key in or up or down or forward or back, in short put some pressure on the key and the switch to try to affect the quality of the electrical contacts as you then turn the key to the start position.
Repeat this several times to see if at least once you can cause the no crank/no start behavior. With the ignition key there might be other behavior, like the dash lights not all coming on.
If the no crank/no start symptom is not intermittent this suggests the problem lies elsewhere. If queried with a suitable Porsche diagnostic computer the car's electronics can report one or more error codes -- such as key ID not recognized -- which can help the tech id what's wrong.
The RFID pill in the key can go bad. (The fact the buttons cause the doors to lock/unlock is not any proof the RFID pill and the associated wiring in the car is working. Two separate circuits.)
Try another key, even the valet key. If no keys work the problem might reside with the car's electronics. The antenna behind the key surround may have a bad connection and the RF signal from the antenna to the key RFID is not being transmitted or the response from the key RFID to the antenna is not being received clearly.