Last tested: March 12, 2021
Toggling off "Allow multiple filter values" on a dashboard filter will limit the filter to "is equal to" and "matches user attribute". This option is located in the "Customize Filter" section of the dashboard filter settings.
Doc on this here.
Another workaround is to use a parameter field and specify several
allowed_valueparameters. For limiting the options in a date filter with this approach, there's an awesome Help Center article explaining that here!
There are two relevant feature requests:
This content is subject to limited support.