Installing the PWA is simple (in Chrome). In the URL bar at the right side on the Lemmy homepage, you should see a little install icon that looks like a monitor with a downward facing arrow. Click that, and it will install the site like an app.
Which instance did you try for that? Lemmy.world definitely didn't have a new reddit feel to me but I can't speak for the others.
I've seen there are some front-ends for desktop that you can use and there are some that make it look like old reddit. I haven't used any of them but you can try this one:
Of course I use lemmy.world, because at first I thought it was the one and only instance.
Maybe I’m wrong in terms of comparing it with new reddit UI, I’m sure that lemmy is way better, but viewing media isn’t as convenient as it was with RES addon.
I’m sure that things will get better soon. Memmy feels like Apollo at its early stages already.