xdelta3: target window checksum mismatch: XD3_INVALID_INPUT
This means your original Rom is false: either wrong size, either version (US, Japan, EU), headered/unheadered etc etc
You need to patch it to the exact same original rom, that the author used to make the xdelta.
and if I disable the checksum validation
DON'T do that - the result WILL be a bugged, non working file. If you disable this, the patch will "turn" the original rom into a hacked one - on wrong addresses!
I think it might have something to do with how I'm using a 7z file as the original platinum rom
LOL, unzip this thing. You can not patch while having original rom in the high compression algorithm.
maybe because I'm using window 10
Doesn't matter which Windows you use - it simply must support the xdelta patcher. If it doesn't, you would know (since the patcher would not open at all).
All in all, you just need to apply the xdelta patch to a clean (unzipped lol) original rom, of correct size, version, header etc and it will work. Usually authors also provide the checksum (sort of ID of the correct original rom to patch to in a form of a long number - aka CRC-32 or SHA, which should be listed in Rom/Iso info and the Header or no header under Patch information).