Yes, if you still have DF gear, or TWW Season 1, you can catalyze it into tier. You can even still do it with Shadowlands catalyzable gear.
What you can’t do is upgrade its ilevel so that you could collect different raid difficulty appearances with the same item. If you catalyze a Normal raid item, that’s all you ever get for that item. You’ll have to find a Heroic ilevel item to catalyze to get the Heroic appearance.
At least catalyzing outdated gear doesn’t cost charges. Just the item and the 5-second countdown each item.