You're looking in the wrong direction.
Let's say you get an electric heater of that size. How would you control it on a thermostat? I promise you in a warehouse where that would be used it wouldn't just be a circuit breaker you turn on and off.
The answer is a relay, AKA a contactor. A small amount of power, either 24 volt or 120 volt at low amperage energizes the coil, which then pulls the contactor and engages a much larger power flow. With such a thing you could use any any thermostat such as a Z-Wave Honeywell T6 Pro or a Smart switch to control the big load.
That said, such an electric heater will use an awful lot of power. You should really consider a mini split.
Electric heaters are about 100% efficient. 5000 w of power input equals 5000 w of heat output. Heat pumps depending on the conditions can be 250% to 400% efficient. That's because they aren't turning electricity into heat, they are using electricity to move already existing heat in from the outside. Thus 5000 w of power input could mean 15,000 w of heat output.
A lot of mini splits work with an external thermostat, but you don't want to use them that way. Mini splits are modulated output, which means the compressor can run at almost any speed from 1% to 100%. They get maximum efficiency when working at about half output. So you want to be able to enable that savings. That means using the mini splits internal thermostat rather than an external thermostat that just switches it on and off.
A great many of them use infrared, so you could just rig up an IR emitter that would send it commands. Then don't use the remote control that comes with it and it will still have whatever state you just broadcast it via infrared.
Alternatively there are some that have online connections and can be controlled via the cloud. For certain ones there is a replacement connection board you can get that replaces the Wi-Fi cloud connector with an ESP device enabling local control via home assistant. Do some research on this before you purchase.