What is missing for SPI?

as written above ... control x595 shift register via SPI ...

That is already clear to me, only PCF8574 is not enough for the reasons mentioned above. I also have different test setups here, ESP32 + ULN driver, ESP8266 + PCF + inverter (because of initial state) + driver (discret and ULN), everything works. Only ESP8266 + TPIC6B595 (+ I2C_sensor depending on t...

For cheap and simple, the PCF8574 also has disadvantages (initial state, max 20ma, ....).

I would like to switch a slightly larger number of relays and solenoid valves (100mA) with the least possible effort ...

Still "somewhat tricky" is a bit of an understatement. That's exactly why my question. There are solutions for everything, but the effort has to match. ESP32 and output driver are of course also possible ... Only for the small 8266 would the possibility of being able to use more outputs s...

Is it possible to implement support for shift registers e.g. 74HC595 or the Power Logic version TPIC6B595 or similar?
Or are there already other possibilities / tricks to connect them to ESP Easy (via rules)?