According to APA (2020), an abstract should typically be around 150–250 words and briefly cover the key aspects of related literature, purpose, methodology, findings, and implications.
American Psychological Association. (2020). Publication manual of the American Psychological Association (7th ed.). https://doi.org/10.1037/0000165-000
Here is a link to download their guide on abstract and keywords.
When I review papers, I expect the abstract to guide me in what I will find in the manuscript as a whole. So, I would be frustrated if the abstract omitted any coverage of the conclusions -- and the last thing you want to do is to irate a reviewer before they even begin to reader the actual paper.