I’m just another guy, not a professional at all. I am, however, a microbiologist that works at a place that tests for this exact thing (but we don’t remediate). So this does not constitute a recommendation. Hopefully an actual remediation person can come in and tell you/correct me so I know. I make zero claim to how the spot will look after, but it should be fine. And so on and so forth.
From a microbiology standpoint, if it’s grown like that, its going to have put spores out everywhere. So while cutting it out and replacing is the BEST option, it’s mostly just going to remove the active production of spores. This can also be nearly identically achieved with a bleach solution. You can buy them premade, but it’s basically just 10% (?) bleach and 90% water. Should be super easy to find exact formula online. Put that in a spray bottle, soak the spot on both sides, let it dry, and repeat a couple of times. Maybe scrape it off with a putty knife and put it directly into a sealed bag before you walk it through your house. Seriously, spores are no joke - some can survive re-entering the Earth’s atmosphere. Don’t walk it through the house open. Respray, rinse and repeat.
If you REALLY want to make sure and give zero shits about how it looks, use 100% bleach after. But know that bleach likes to dissolve things - it’s basically the same as an acid, but in the other side of the chemical spectrum, and has the same results. I’d check online to see how drywall will react before doing this, but it’ll kill the fungi/mold.
Once you’re satisfied that the spot has been touched by bleach all the way through, paint it and forget it exists. It’ll let you know relatively quickly if you didn’t get it all.
Again, this is from a microbiology standpoint only. I have no idea how the drywall will react or have any experience in remediation.