Homemade garum is a fun kitchen experiment, if you have the equipment and patience. Heat + protease + protein substrate is really all you need.
it hasn't updated in a while but i quite like this blog: https://www.culinarycrush.biz/all/will-it-garum
Please, for the love of all that is holy, do not make this if you have neighbors.
https://www.youtube.com/shorts/R1Hq3WEqVeI
The video claims the smell is not "entirely unpleasant" but that's a lie. It is the most disgusting smell I have ever encountered. And I used to have to shovel manure and clean chicken coops growing up. Once I even had to dig a dead racoon out of the guts of a square baler after it got run over and jammed up the machinery and then sat for a few days in the summer heat. Garum smells worse.
On that note, the easiest way to get your hands on some protease is to buy digestive enzymes sold as food supplements (most often they're made out of dried pork pancreas).
You also don't need much equipment: scales and an immersion circulator should do the trick.