Yes, yes. Flash (with AS3) was a first-class web application platform. There were buttons and views and "movie clips" and other stuff for you to place on a blank canvas, all very customizable. Then there was Flex, a full-fledged yet relatively lightweight application framework built on that foundation. You created your layouts with XML, with live preview. There were Android-like layout containers (emulating Android's LinearLayout with HTML+CSS is still not quite trivial in 2022 — the defaults on flexbox are bonkers) and there were ListView/(UI|NS)CollectionView-style lists with reusable cells, among other things. This was 15 years ago! I can't even begin to imagine how many workarounds one would need to implement a list with reusable cells with HTML+JS even if targeting only the latest Chrome and Firefox.

HTML is a document format at its heart and there's no getting around that, but <object> is/was a nice escape hatch.