The simple way to do this is a dumb thermostat wired through a relay coil that enables a fan. It doesn’t give you remote access to change the setpoint but that’s all this setup does. Something like this has a setpoint you change once and then leave it.

For specific applications like transfer fans for a server room with a small amount of heat to react, you can buy an all-in-one thermostatically controlled fan: https://acinfinity.com/room-to-room-fan-8-with-temperature-c...