Are scientific contributions of the article listed in the abstract? As the title says. To put the contributions (explicitly) on the abstract:

Is considered good practice
Irrelevant as long as you correctly describe your paper? Source Research Guides
No, explicitly mentioning the contributions is not considered good practice and should be avoided.
Other?

Here is an example of a paper I published on ArXiv. Would you say that the abstract is Ok? Please see I put the main emphasis on the contribution (I use the contribution as an excuse to then explain all the work done).
NOTE: Please don't confuse with the contribution of each author to the article! An article should have something new, therefore we can say a contribution to science.
Some article's have a specific section for that reference. Others just mention it reference but my question goes if it is good to mention it in the abstract or not.

As this question is somewhat subjective and there might not be a CORRECT response. If after some time I consider fit there is not a precise justification (some indisputable reference for example) I will mark as a solution the response that had more upvotes, supposing the upvotes reflect what the community thinks.
In light of the example you linked, you should indeed state your contributions, but there is no need to state that these are your contributions. So instead of stating &quot;The contribution in this paper is considering problem A using method B&quot;, you should use &quot;We consider problem A using method B&quot;. Doing this would have easily saved 20 words in your example without changing any of the meaning. Even more importantly, the useless words are in the beginning, which is the only part of the abstract you can actually be sure that people will read.
The default assumption on a paper is that you are presenting something new and that new thing is why people should be reading your paper, which is why will be prominently mentioned in the abstract. So the default assumption when reading an abstract is that all results mentioned describe scientific contribution. There is thus no need to explicitly mention it.
There are of course things in the abstract that are not new contributions, but they are generally made obvious by phrasing. If your abstract starts with &quot;We survey some recent results in ...&quot; no one expects that the results mentioned afterwards are new. Or if you are (in)directly referencing using &quot;The well known problem of ...&quot; then no one will think you came up with the problem. But if a sentence starts with &quot;We show that ...&quot;, then any reader will assume that you claim to be the first one to do so in this context.