Seems like this bug is still in existence - it was reported in 2020
Pagination on lists don’t work - Get Help - Adalo
I’ve tried re-creating my custom list, adjusting it so that it’s not in a container and ensuring it’s the only thing on a screen, but still, despite being set to load items on scroll, it never loads beyond 20 items. I have no choice but to set the list to load all items, which has the potential to be very slow. From what I can gather, load on scroll always loads 20 items in its initial database pull.