The previous 4/6GB RAM configuration has been lifted to 8GB - and for the most expensive 1TB and 2TB models, has increased RAM to 16GB.
The new model iPad Pro models have lifted the bar - allowing the iPad to operate much more efficiently with large datasets. The second is working with data to cite an example, such video editing, a considerable volume of data needs to be loaded for manipulation - and this needs RAM, particularly when loading multiple video streams. The first is fast task switching iOS/iPadOS does not use full pre-emptive multi-tasking, but does keep active and loaded-inactive processes in RAM to allow rapid process switching. The iOS/iPadOS system architecture keeps processes in working memory (RAM) for two reasons. For this system architecture, un-utilised RAM (spare) is wasteful. IOS/iPadOS has very efficient memory management - that, contrary to what you might expect, is designed to continuously utilise as much available RAM as possible.