Are their any benefits, if a recent PhD graduate have too many peer-reviewed publications as first author?

Too many first author publications can raise questions as to how one can be that productive. Within any field most researchers know what it takes to achieve a publication and as such having too many first authors could raise questions as to who actually did the work or wrote the paper. It may also signal that the graduate may not have spent enough time with the fundamentals of establishing independence and running a lab rather than seeking publications.

Having a lot of published papers as a first author shows, that you were successful during your Ph.D. Hence, it increase your chance of getting a better job as a next step, especially in the academical sector. 

Obviously, both first and last authorship represent a greater emphasis for the researcher, as it implies greater responsibility for the publication.

Yes, having many peer-reviewed publications as a first author can enhance a recent PhD graduate's credibility, expertise, and competitiveness in academic and professional settings.

Depending on what is meant by much. A PhD student have to focus on his PhD work and not to be involved in many different works. So, the publications he/she publishes as first author are coming out from his/her work and according to my 30_years experience as full-time researcher this connot exceed 2 (or at most 3 in some fields like computer science or mathematics ou theoretical physics) papers per year. So having too much paper is a bad indication  nd could be interpreted as a sign of scientific misconduct or lack of integrity. 

It usually depends on the quality of the publications and whether the PhD actually participated in the  design, execution, interpretation of results, discussion and/or in the writing of the manuscript. Assuming that the journals in which the manuscripts were published are all reasonably respected, the PhD will likely be questioned on each of the publications so that the interviewers can certify that the PhD contributed intellectually to the design, execution, interpretation of results and/or in the writing of the manuscript and thus has deep understanding about all publications. If all of the above are true, then having many publications is great and will positively contribute to lending a good job.  

It is difficult to define what is "too many".

It could indicate success/productivity, but it's also not 'the more the better'. Quality over quantity. If I would e.g. need to hire a postdoc and a potential candidates has many more publications than expected based on their career stage I would definitely want to know the reasons for this and critically look at e.g. quality of the papers, journals in which the work is published, is it all on the same topic or using similar methods or diversity, is everything with the same team or does it reflect multiple collaborations, if there is any 'salami slicing' of datasets, etc.. Also; i would critically check and ask about other experience: did the candidate 'only' publish papers or also teach, organize scientific events, present at conferences, supervise students, etc., etc. There is more to scientific CV than only publications.  

Having many first-authored publications as a recent Ph.D. graduate is predominantly beneficial, but it's crucial to maintain a balance and prioritize quality research alongside quantity. It's also important to consider potential drawbacks and ensure ethical authorship practices. Remember, a successful research career requires a multifaceted skillset, and publications are just one important piece of the puzzle.

First authors for publications are usually prestigious and add credit to career advancement. Most first authors do the donkey work and are the ones that get involved in the research work. If your field allows having many publications as the first author then it is advantageous for recognition and expertise. However, too many would raise questions about one's intent and the credibility of the publications especially if the interval is close. 

You cannot have too many papers as first author. The more, the better.

Yes it will create a better opinion about the candidate appearing for any position where research publication has immense value.

 A few impactful, well-conducted first-author publications can be more valuable than numerous rushed or less significant ones

Multiple first-authored publications in respected journals show that the Ph.D. student has a good work ethic and an advisor ready to fund multiple projects.
It is a good thing as it places the student in a good position to obtain faculty or post-doc positions after their studies.

Yes, one with numerous peer-reviewed publications asd first author benefits from enhanced academic credibility, increased job market competitiveness, and greater opportunities for research funding and collaborations.

Obviousely, being a first author gives great chances!

Yes, having numerous peer-reviewed publications as a first author, especially in journals with an impact factor greater than 5, can bring substantial benefits for a recent Ph.D. graduate. Such prolific publication records are unusual, enhance the graduate's visibility within the academic community, potentially leading to increased collaboration opportunities and invitations to conferences. It can strengthen your competitiveness in securing research grants, academic positions, or industry opportunities. 

There can be several benefits for a recent PhD graduate to have many peer-reviewed publications as first author:

Sure, it increases their chances of getting a postdoctoral fellowship.