as someone who didn't like the new theme when it first launched and switched back, there seems to have been enough improvement to it that i have trouble remembering what it was about it originally that i didn't like
much improved so i'm sticking with the new one for good now
The new theme, whether in light or dark mode, only highlights hyperlinks if you hover the mouse over it/them.
FYI you can ignore this as it was only an issue in preview mode. Once you actually submit the post the hyperlinks are clearly visible as blue links in both dark and light modes of the mobile-friendly theme.