I’ve stuck the continental explorers on our littleginge’s 20″ bike after spending a bit of time seeing what else is out there. The Rocket Rons would probably have been my 1st choice if they hadn’t been so ridiculously expensive as they are ~100g lighter and probably compare reasonably well in terms of volume/grip.
The only other ones that I found that looked like they had considerably more aggressive off road tread patterns were the crown gem and flow snap from Vee. However, they are all pretty hefty and not easy to find in stock anywhere the last time I tried looking (they do have folding and/or tubeless options in there though)
Looks like the 20 x 2.4 tubless flow snap tyres are in stock at amazon, nearly £40 each though:
20x 2.4 Vee Flow Snap