What are my options if I want to install a bed levelling sensor capable of operating at 100 °C? I currently use a BLtouch 3.1, which is known to stop operating at about 35-40 °C. In fact, when I preheat the bed at 100 °C close to the probe, I sometimes get issues with the pin not retracting correctly.
I would like in the future to enclose and heat the printer chamber, therefore I need a probe capable of operating at higher temperature. My target is 100 °C.
As of now, I'm aware of this solution:
https://hightemp3d.com/products/remoteht-bed-level-probe-3d-printer

This high temperature probe uses a mechanical switch in combination
with a servo motor to probe the bed. The servo motor is outside the
enclosure and retracts the probe pin by pulling on a steel string
inside a spring guide tube.

Microswitches are known to work at high temperatures (that's what the link above uses), but usually need a servo or other mechanism to extend/retract them when needed. Servos typically don't operate at such high temperature, not to mention that they are usually not very accurate.
I saw a Hall filament sensor which uses Hall effect sensors &quot;ss49e&quot; and which could be easily modified to be used as bed probe. Those Hall effect sensors are rated up to 100 °C but at that temperature they have up to 8% shift of the null value and +3/-9% change in sensitivity. The linked project uses two of them in differential mode so the temperature compensation should be much better, but it is not clear how much better. A discussion about it on a Russian forum does not talk about this.
Are there other options operating at 100 °C?
Have you considered using or adapting Prusa’s P.I.N.D.A. V2 or SuperPINDA? Seems that within some bounds they’ve solved the temperature compensation issue.
The older P.I.N.D.A. V1 sensor seems to be temperature-sensitive. See more information in P.I.N.D.A./SuperPINDA Sensor testing article of Pruse Knowledge Base.