ESP8266 and Interrupts - not possible?
Yes possible, but the ESP8266 only has one core and one set of peripherals. WiFi uses time, interrupts, and even the ADC peripheral, and maybe more.
This is why anything timing-critical, or time-intensive, is a pain to get to work properly on an ESP8266. It depends one what you are trying to do, of course, and also on if you can unload what you want to a peripheral the WiFi doesn't use, or if switching off WiFi is an option during parts of your code.
Generally, for applications such as yours, I would get an ESP32 or an Arduino Nano 33 IoT or any other solution that has a core for handling WiFi, and a core for you to use without restrictions. It makes development a more pleasant experience.
If, for some reason, you are bound to using an ESP8266, you would have to be more specific about what your eventual goal is; maybe a workaround can be found.