Yes, as stated in my post above, there is a way to extract the end date in a formula. However, you must set your formulas into another Date/Time field in order to perform any record filtering with them. You cannot filter records based on a formula.
Because of this, your formulas break down when the user decides to select a Single day event, ALL DAY, and furthermore, ALL DAY with repetition or multi-day. There is too much variation for these text-based formulas to work.
With some custom code and additional fields, you can control the date format and extract the end date with formulas, then set another Date/Time field to the end date based on a formula. Then you can finally use that field to perform end-date filtering on your records.
All of this complexity and extra work…just to allow a multi-day event to show up in Today’s Events list!
So I guess the feature request would either be - allow end date to be easily extracted for all user choices (such as use of the Date Formatter function), OR fix the Date/Time field and the calendar view so that Multi-day and repetitive events show up when filtering by days other than their start date.
Hope that helps clarify what’s needed here.