Thanks for the guidance Joe. Spent some time researching what you have said and I came across this unit. Not fully sure how it operates but looks like a cross between an inverter and a buck converter?
Does this fit with your description of a MPPT Heater element controller, but seems to have charger in the title as well.
https://actii.pl/en/ladowarki-prostowniki/979-mpm-pwm-heater-charging-controller-for-solar-solar-panels-actii-ac7391-6931240073919.html
Peter