If u have a grinder or a Dremel tool, make a slit in the screw so that u can use a flat head. Or if u have a screw extractor bit, that might work too.

Since you want to discard the lot to replace it, you are free to hack anyway you can to free it up. So you could use a hacksaw to cut through the plastic and metal starting at the threads just inside the toilet tank, or you could cut through the plastic lever arm enough to free the set-screw up (and then use pliers if needed).

Hey I didn't include this in my photo but the metal rod you see extending through the piece with the screw stuck in it goes all the way to the handle which is broken, so I'm assuming I wouldn't be able to cut through with a hacksaw.

I think I'll try the second idea though I'll just have to find my hacksaw lol

Sadly I don't have any of those :(

That's why I said "plastic and metal" and yeah a hacksaw with a blade intended for metal should do just fine on that, it's not like that metal rod is titanium ... but sure, try the other way first, no problem, might be easier.

Oh didn't see you said that, thanks for the help. Will give it a go tomorrow:)

Zipcut blade on a grinder will have it off in 10 seconds. The a quick trip to HD for replacement parts and you are good to go.

That is likely reverse threaded. Try turning it the other way.

The screw? Crazy lol I'll check later

Any reason why they'd reverse thread it?

Toilet flush handles are reverse threaded so they don't loosen up with each flush, which is a counterclockwise turning. Instead they tend to snug up if anything because of the reverse thread. This is due to the standard handle placement on the front right of the tank.

Cut through the white plastic flush arm parallel with the spindle. Once it's through just prise it off unscrew the plastic hex nut on the inside then replace the whole thing.

Its just brass it will easily cut with a hacksaw

Ohhh that actually makes a ton of sense thanks! Btw there's no way tanks are usually this dirty? I haven't looked in there in years I just forgot about it.

Is it a hazard? There's literally weird blueish green foamy dust everywhere

Always wear safety glasses with these things. You don't wanna trust a safety squint when a disc spinning at 10,000 rpm shatters and sends shards flying in all directions.