I don't have the app and I use reddit (although not often) via my mobile browser (firefox) and it never forced me to download the app, as far as I recall.
I encountered that blocker today, so I decided to try Safari's Hide Distracting Items (1) feature, which blocked it once and for all, which I was pretty impressed by.
It does it occasionally to me (Safari on iOS). When it happens, I just close the page. I hope this is enough of a signal to make someone think.
I land on Reddit every couple of days or so, and if they don’t kick me I read the thread and sometimes browse a bit a couple of subreddits I used to participate in.
I started getting a blocking overlay telling me to download the app on new reddit and I just leave.