I tried another way.
In iOS or iPadOS, simulating a hover-action by touch does not seem to work. But I find a setting in Settings -> Accessibility -> Touch -> AssistiveTouch -> Pointing Device -> Mouse Keys. What you need to do just turn on the Mouse keys so that you can move the mouse pointer by using the keyboard.
Now I can move the pointer to hover the internal links I want to preview, and it actually work. But a new problem comes, that is when I previewed a pdf page, I couldn’t change the current page of it, the preview pane will disappear when I click or tap the > and ‘<’ buttons.
Most importantly, I don’t want a keyboard is indispensable every time I read my notes. I hope Obsidian could adapt Page Preview core plugin to the mobile in the future updates, or if anyone could teach me a better solution, I will be very appreciate with you.