As the conjugation is a subjunctive, one can eliminate :

• Il paraît
• Il est certain
• Il croit

(and by the way, ‘Il croit’ means ‘he believes’ : it’s not an impersonal form like the others).

Note that all those 3 forms would be acceptable with an indicative (future because of the ‘bientôt’), for example :

Il paraît que les trottinettes seront bientôt interdites sur nos trottoirs

So the only valid one is :

Il est possible que les trottinettes soient bientôt interdites sur nos trottoirs.

Here are some other elements that would fit in here :

• Il semble
• Il est à craindre
• Il est souhaitable

As for the why, it’s dictated by usage, and there a lot of exceptions but :

• For a possibility or a wish, it’s mostly subjunctive mood.
• For something certain or obvious, it’s mostly indicative mood.