Is there support for a temperature probe wired directly to a Raspberry Pi GPIO or I2C? If not, there should be since it shouldn't be necessary to use an Arduino for the task.

I2C and SPI yes, direct no. I am investigating Astroberry DIY as a way of integrating different temperature solutions including internal as well as external.

You can attach, e.g. a BME280 sensor.

I have some scripts here, to do environmental monitoring of my imaging sessions, as part of Astroberry's panels:
github.com/jscheidtmann/astroberry-serve...panel/files/envpanel

I have not created an INDI driver and do not intend to create one at the moment.

Best regards, Jens

Thank you Jens. Is Envpanel supported by the EKOS weather monitoring and for refocusing on temperature change?

No, that would mean to write an INDI driver. I have currently no plans to do this, as I am building an Ardufocuser, which will also include a temperature sensor...

Maybe this here helps: Radek supports another sensor in the astroberry-diy driver, see here: github.com/rkaczorek/astroberry-diy

So the Astroberry DIY driver is excellent, but is not compatible with my motor driver, a Waveshare Stepper Motor HAT that is based on the DRV8825. Perhaps I will ask Radek to add support for it.
But I still believe an INDI driver for sensors installed on a Raspberry Pi without an arduino in between is desirable.