Cut sections of drywall ~3” wide and glue/screw around the hole so that 1/2 of the pieces extend into the hole to support the patch. Then attach the patch, so it’s supported all the way around as well as to the joist. Then finish it out.

You definitely need wood blocking behind those long edges.

So i actually need to replace the entire sheet, so i can anchor the entire edge?

Start talking in details. What’s the size of the cut out. Where are your nearest joices in inches. This will Allow detailed accurate responses here.

There's nothing behind the edges, where you see screws are where the joists are

Take out the drywall, cut some squares of plywood and fit one to each corner of the hole so it bridges between the new and old drywall. Screw it down to the old drywall, then fit the new piece and screw it in too

I think what was meant was to pull the drywall patch and take a 2x4 cut to length on each side sistered to the framing that's already there. You then screw the drywall into that sistered wood to support the patch. Basically you are trying to make the new drywall piece as strong as the full sheet by screwing it to the wood.

The old drywall crumbled las time a drill touched it, which is why I am a little nervous affixing anything to it.

Put a little piece of wood above on the 4 corners, half way behind the old and halfway out where the new will attach. Run screws into the wood through the old board (hold it down above so it won't raise up with the screws), then put the new piece back up add screws to those 4 corners and to all the places you have them now - and you're good to go.

Go to your local lumber yard and buy a piece of 1"x3". Cut pieces to fit the long edges and place them with 50% overlap above the existing drywall. Screw each piece in using drywall screws. Install your filler piece, I would suggest to place the screws about 6-8" apart. Use dry mix compound (Sheetrock/Durabond) for the first coat. https://www.homedepot.ca/product/saint-gobain-adfors-250-ft-fibafuse-drywall-tape/1000754764 Fibafuse is premium drywall tape and is better for butt joints. 2nd & 3rd coats can be premixed mud if you wish as it sands easier. Good luck.

If all 4 sides of your patch are supported, you are good to go. Use setting mud, and fiberglass tape for your first coat.

Put in an access panel

I don't really see that you have a choice. The patch as-is doesn't have enough support, you either need to support it or replace more of the old drywall until you get back to studs

Thanks. I think you're right but was hoping this wasnt the case

This was my first idea! Im too concerned with putting any type of load on the existing drywall and the joist configuration will make it difficult, but i could hand something, right? I even bought some light molding to frame it to hide the edges. How would you start?

What about creating a portal to access this spot in the future. I did this for a friend of mine who had rats above his ceiling. He didnt have an actual attic bc it was an apartment. But we made a latchable hatch so he could get the dead rats out but not to have an open hole so the rats jump into his bedroom. Long story long, you might need to get back in there one day

Actually, I meant gluin and screwing 3” wide lengths of drywall on top of the existing drywall (patch removed first) on all four sides so he could attach the patch to them. I’d also suggest he cut away the paper around the patch a couple inches for the new paper to lay flush.

Dude needs to cut back to sold drywall, otherwise the repair will be crazy obvious.

Your suggestion works, but it depends on if the cutout was flush with the framing because there wouldn't be room for the drywall overlap on to the existing drywall for at least part of the patch if it was because the wood would be in the way.

YouTube “That kilted guy” for taping and finishing. The number of videos he has is little overwhelming, but one of the best resources for finishing joints I’ve used.

That's funny - I have a plumbing issue downstairs.

You can try to find a vent that opens to cover the hole and if you need access again you can just unlatch and open. Seen this a few times before. Looks like a ceiling vent but surprise access to pipes !!! I say this because it will look more natural than a regular panel !!

You're local big box store will have various plastic spring loaded panels available. Easiest solution and maintains access if you need it.

This is my route. Large access, but the alternative is an entire new dry wall panel i think.

Then use elmers glue to bond the wood strips to the old drywall.

This isn’t very complicated. Perhaps look up on YouTube how to patch drywall? As others have said, you definitely need blocking across each edge. If the drywall is crumbling, as you said, why? Did it get wet? If it did, you may need to cut out the section that has lost its ability to hold a screw. If it’s the whole sheet, so be it. They’re like $15-$20 each. Not worth breaking your head over IMO

If those drywall screws are into wood, what's the issue? Just tape and mud it