For analog electrical simulation there's SPICE. Kicad has a spice tool built in, but I haven't used it. It has some improvements in Kicad 6. I use LTSpice.
For digital or systems simulation there's Renode. You have to recreate the system in Renode,there's no Kicad integration.
For digital or systems simulation there's Renode. You have to recreate the system in Renode,there's no Kicad integration.