If you try to write a rule in Portfolios using a Custom Date field, the rule result options you get are only " X number of days into the future".
This is unusually restrictive. We definitely need more options than this.
If you are in Project rules, you get a LOT more options with rules on Custom Date fields, including the option that we need for our purposes in Portfolios. We have one custom date field in our Portfolio that always needs to be set to January 1st, 2025, for all projects, for all reasons, at all times.
I can do that in a project (set a rule that changes the date to 1/1/25) if the date is changed to some other value.
I need to also do that sort of thing with that same field in a portfolio.