It rarely does. It saves instances of the main page, but the deeper you go in, the less links are saved for each instance. I was a member in a similar PHPbb forum and out of around three thousands of my posts I could barely find a hundred after it went down. Similar case with another custom made forum. I lost 8000+ posts there.
Iād expect that the only useful things left will be the cases of topics that were ātop-heavyā, like guides or collections of information and resources.
Example in OGS:
The rest, that would require multiple pages to be archived to be useful, will mostly become a slog to go through or will have significant portions missing.
I havenāt checked how OGS forum gets archived, but with its way of loading the posts, it might appear that the pages are saved, but once you start scrolling, they might be mostly empty/not-loading.