I thought the only tags available were the ones that showed up when you started to type search criteria in... sorry
I thought so too ;-)
Itch has a lot of quirks. People new to the site might expect certain behaviour from certain features based on previous experience on other sites with similar features.
I remember a very heated discussion about the wording of (View all tags) . Literally one would expect to see, well, all tags there. But it ain't so. And the page itself says "top tags". But the link there is on all browse pages and worded misleadingly according to my non native understanding of English.
And interestingly, that page (view all tags/top tags) has a section called Platforms. https://itch.io/tags/platforms Which lists 26 platforms, but Windows/Linux not among them...
Of course the "Find tag" box above will actually not find tags. It does not search the existing tags, it only searches and finds the tags listed in the tag box, that are called suggested tags in some places.
For my OCD, some of those quirks are ... quity itchy. (pun intended). Imho it should read "view top tags" instead of "view all tags", on the browse page. And "find popular tags" on that toptag page instead of "find tags". And it should read "select/write a tag" instead of "select a tag" in the browse tag box. Or any other wording wich carries the same meaning.