If you're waiting for 16GB of RAM on the Note 20 Ultra, that is not available and I don't think that is going to be something they will offer. If that is your want and need then you can go with the S20 Ultra. But you shouldn't really need that much RAM. There isn't much you could do with it. Your decision between the S series and Note series shouldn't be based on RAM.
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I would re-evaluate your need for 16 GB of RAM. It would be an extremely rare case where 16 GB vs 12 GB would provide a user any noticeable difference in operation.
I disagree with your opinion because running into high RAM use is possible for Dex users. you're right that there's no need for a high RAM configuration for using the phone in regular use. someone using dex while streaming lectures, recording, and taking notes all at the same time - something many college students have a need for - means that 16 gigabytes of RAM is not a niche use case.
Sure there are cases and it is easy to speculate on situations that might require more. Have you had a chance to run this scenario on a Note 20 Ultra and check the RAM usage?