I excluded some tags in the new settings and try to preview the digest email, the preview contains some duplicated topics, and topics with those tags are also included.
Testing this on my local dev site, it seems to be a bug. The code is expecting the digest_suppress_tags setting to be a pipe delineated list of tag ids, but it’s actually a list of tag names:
Here’s what the setting looks like on my site:
SiteSetting.digest_suppress_tags
=> "foo|bar"
The code that’s excluding the tags from the digest is expecting the setting’s value to be "1|2" (the tag ids.)
Note that the digest_suppress_categories setting works without any issue. The settings category-selector saves category ids, not category names.