Yeah, as far as actual plants go (not macroalgae), your choices are severely limited. There are like four species of marine grass in the hobby (one of which is coldwater), and you can do mangroves too (there’s like three species of mangrove, you typically see red and black mangroves in the hobby). That’s about it.
You might be able to find some other plants that could work if made a little “beach” area in the tank, but those sorts of plants are generally pretty difficult to keep as I understand it (too much water/salt and they die, too little water/salt and they die - given where they grow, it’s a very delicate balance).
From the macroalgae side of things, there’s a decent number of options (including some “pest/invasive” algae species that are quite pretty). It’s definitely a bit different than running a reef tank, though, and - if I remember correctly - it can be fairly difficult to maintain long term. A few people keep them, though, and they’re quite nice looking tanks when kept tidy.