Apple don't tend to upgrade the Ram in the 12.9" Pro that often. The 2015, 2017 iPad Pro's (12.9") had 4GB Ram. In the 2018 redesign, it was only the 1TB version that got 6GB Ram. In last years model all the storage options got 6GB.I switched my 2018 for a 2020 just because of the RAM increase, so if so we’re on a 2018 I’d update to the 2021 for sure.
I'm not sure if Apple will increase it to 8GB this year, they may hold off until next year or even the year after. However if they have plans to bring Final Cut Pro and Logic apps to the iPad Pro, then i think they would up the Ram and possibly the storage (maybe 2TB storage and 8GB Ram?).