When viewing a user's activity there seems to be a discrepancy between all / replies and topics. The former show (partially) the content of a post while the latter does not.
Is there any reason for that?
I can imagine the logic of the designer:
A reply is a post, so it makes sense to display an excerpt of the post.
A topic is a container for multiple posts, so perhaps it is logical to treat it differently from a post.
The "All" view is a mixture of topics and posts. It would look messy if the items were treated differently, so the post excerpt approach is applied universally.
That said, the first post is where the topic creator introduces the subject of the topic, so an excerpt of that post can provide valuable information about the topic, which may not be obvious from to title alone (new users tend to be bad at writing helpful titles).
I never noticed this before which made me wonder if it might be a recent change. I did a quick look through the pull requests in the Discourse repository:
https://github.com/discourse/discourse/pulls?q=is%3Apr+activity+topics+state%3Amerged
and didn't spot anything.
I also asked the Ask Discourse AI chatbot provided by Discourse about it. It said it believes it has always been like this.
Of course neither of the above are conclusive. Searching for changes in codebases can be challenging because the keywords I think of as a user may be different from the terminology used by a developer in their commit/PR message. And of course AI is prone to providing incorrect information (though I do find Ask Discourse to be quite good).
In the case where community members identify something they think could be improved in the open source Discourse forum framework, they are welcome to submit a feature request to the Discourse developers:
The same goes for any defects we might identify:
I have found the Discourse team are generally quite receptive to feature requests and bug reports.
In the case you aren't sure whether the deficiency/defect is something specific to the Arduino Forum instance, or general to the Discourse framework, you can perform tests in a vanilla sandbox Discourse instance that is provided for this purpose:
If you see the same deficiency/defect in try.discourse.org, then you have determined that it is from the Discourse framework, and thus eligible for escalation to the Discourse team.
In order to avoid wasting time by raising a duplicate, please make sure to search the existing topics in the "Feature" or "Bug" categories on the Discourse Meta forum prior to submitting a report.
I did see the same behaviour on meta.discourse.org 
I've now asked the same question there: Discrepancy in display of user activity (all / replies vs topic) - UX - Discourse Meta.