There is a big broblem SE wide in my view where not all hints, tips and pointers are on view when posting or reading via an android or iOS app. The same goes when viewing in a mobile browser.
One example is that MedicalSciences.SE has a big problem with this too and they have a big discliamer on the top right of the main Q&A page which I have asked in the past about having here

This is viewable on a computer and visiting the MedicalSciences.SE site in a computer browser, but when viewed in my mobile phone browser I get the following:

With regard to the pop-up for new users, after thorough testing as you pointed out in the comments, the pop-up comes up when visiting in a mobile browser. There is however an issue with the StackExchange Apps. The pop-up does NOT show in either the iOS or Android apps.
The best course of action in my view is to post a request to meta.SE as suggested by @AliceD and continue as we are at the moment which is to vote close with a comment.
I have a standard comment I use for this situation which is:
Welcome to Psychology.SE! I am sorry, but for a number of reasons outlined in this meta post we can not, and will not, give advice or potential diagnoses for any specific individual. If you or anyone else has a question regarding personal mental health, advice from a doctor should be sought. For further information on how this site is supposed to work, what is on-topic or not, you can take the tour, visit the How to Ask page and Psychology & Neuroscience Meta.
there are shortcodes you can use to help so the markup used when posting the comment is:
Welcome to Psychology.SE! I am sorry, but [for a number of reasons outlined in this meta post](https://psychology.meta.stackexchange.com/questions/502/why-was-my-self-help-question-closed-as-off-topic) we can not, and will not, give advice or potential diagnoses for any specific individual. If you or anyone else has a question regarding personal mental health, advice from a doctor should be sought. For further information on how this site is supposed to work, what is on-topic or not, you can take the [tour], visit the [ask] page and [meta].