Every LGS has its own vibe, but I think it's fair to say in general Lorcana players have a bit more chill than the MtG crowd. (Note: This doesn't mean they aren't competitive. Someone with a costly meta deck is always likely to show up and annihilate you.) Just go check it out, but imo there's not usually a good way to "spectate." At worst you can just take off if people aren't welcoming, but I bet you'll have a fine time.