Preprints are defined as an author’s version of a research manuscript prior to formal peer review at a journal, which is deposited on a public server. ResearchGate (RG) said about "Preprints": early-stage research. On the other side, RG is not a publisher and, in turn, uploaded unpublished text is not regarded as a publication. Hence, a preprint is an author's own original or draft version of their paper before any peer review has taken place and before it is published.
Before answering this valuable question of Prof. Shin Murakami, please let me give my own opinion about the preprint dilemma (مُعضلة ما قبل الطباعة):
I have a different perspective on uploading any preprint anywhere before it has been published. Why do you let others know about your insights and methodologies before publication? You should avoid telling the other researchers about the details of any one of your papers until it has been published and seeing your name by yourself. You may say that I am somewhat old-fashioned, but I have a different perspective on uploading any preprint anywhere before it has been published by your name. My advice is not to put your research anywhere until it is published. It is a security issue:
Your manuscript may be copied and then published by others before you can do that. This stealing of your paper might be happening. So, you must wait until the paper is accepted and then published in that journal. Then, upload that research item on any platform you wish.
A journal may have automated plagiarism software to check the paper before admitting it to the reviewing process. There are chances that your paper can get a rejection at any point. Thus, to avoid this problem. Publish the preprint after you got the paper as "ACCEPTED".
There may be a "cold war" between the professors of a given department. They do not like to discuss ideas as others will "steal" them and publish an article on them without giving credit to the one from whom they got the idea. My suggestion is to keep your work "private" and share it only with those who are really interested.
Academic publishing remains a competitive process. If someone else has recently published a paper very similar to mine, mine is less likely to be accepted. So although I may share my topic, I prefer to keep my methodology, findings, and discussion private, until published in a peer-reviewed journal. So. there is a high chance that someone may claim your idea as theirs!
Preprint gives a false feeling of security. Personally, I would always wait until the paper is accepted by the editor of a journal. After that, I can post it as a regular research item on any platform you wish.
Finally, for the coming future, do not upload any paper anywhere until it is published with your name. Even if it is a "preprint"! For the time being, If you had done something like that as a "preprint", for instance, I advise you to delete the preprint from any elsewhere and wait for two months before sending the paper to any journal.
One of my friends was accused of plagiarism; do you know why?
After about three months, his research paper was rejected because of plagiarism. When he checked the journal report, he found that his paper was accused of plagiarism with a 61% percentage. The reason is that his manuscript was previously uploaded as a preprint. It took him another two months to solve the problem and remove the manuscript from the database of the preprint.
So, in order to solve this type of issue, it may take several months of following up to remove the manuscript from the database of the preprint. Anyhow, If there were accusations of plagiarism, it is not well for any researcher's reputation, in any meaning.