if its a freebie fridge freezer its worth a punt, simply plug it into the inkbird cold socket and a heater in the fridge too.
I would mount the heater away from the freezer and add a pc fan to blow over the heater directly. And stick a max/min thermometer in the freezer during brew #1
it will tell you how the freezer section reacts to brewfridge control, and if the freezer will be viable for food storage,
to be on the safe side run it as a fridge freezer for a few hours/overnight before plugging it into the inkbird @ the target temp and adding a brew.
you will probably find brewing ales @18c will have a knock on effect to the freezer and warm it up as a consequence.
Now you may be able to counter this by adding insulation to the fridge bottom/freezer top?? but test with something removable first as when it comes to crash chilling or lagering you may wish to remove said extra insulation.
edit** bin bag full of vermiculite or perlite would make a good easy to fit bottom of fridge insulator
Folk have come a cropper trying to build a 2 chamber brewfridge from a fridge freezer and afaik most attempts at that have been a massive fail.
I think it may work well enough for dog food however especially if you load the top shelf of the freezer with ice water boxes as a cold store too..
go for it....
if the freezer compartment gets too warm during a brew. a more hands on hack may be doable but it depends on the fridge freezer..