In old times calibrating a power meter was as easy as connecting 1x, 2x, 3x high power halogen bulbs to get realistic data, free of reactive power or strange waveforms with strong harmonics.

Nowadays simple heaters are not common (I have no electrical room heaters, for example) and light bulbs with LEDs produce harmonics which may affect the accuracy of a power meter, not to mention that calibrating a 2+ kW meter with 5-15 W is unrealistic.

I read online that motors are not suitable for the calibration, therefore hairdryers don't work.

What can I use, easily available in households in 2020 and which power I can accurately estimate with other means, to calibrate my power meter based on (according to Tasmota codes) "HLWBL Energy Monitoring" and "BL0937 Single Phase Energy Monitor"?

Concerning the tools, I have a multimeter which I can use to measure resistance, voltage and current values.

Concerning the devices, besides normal household ones, I also have more unusual devices like an about 80 W terrarium heating cable and a 750 W silicone heater for 3D printer, which however, contrary to the terrarium heater, is not meant to be operated without temperature control (it is meant to be overpowered).