There are already a few good posts in here detailing what you asked, but I'll just add that on any given day or night, any 1/2 game in Las Vegas can be full of weak passive fun playing types.
At the same time, any 1/2 game can be full of headphone *******s who are there that day for whatever reason.
Typically, avoiding the bigger and nicer rooms will tend to be better to start out feeling more comfortable and less overwhelming. Some of my favorite spots that fit what you are looking for are Flamingo, Ballys, Sante Fe Station, and especially Excalibur if you want to time warp back into games where nightly there will be players who have never played NL poker live in a casino before.
Sure, as with all rooms, any given day can yield very different types of games, so don't be surprised to show up to a small room and sit in a 'terrible game'. (Backpacks, headphones, fish beraters, try hards where there are more 3bets in 2 hours than you might see in an entire month of play at 1/2, etc). It's just that, on the whole, you find a lot less of that in the smaller rooms.
Orleans for NL is nice because when the bad beat jackpot gets big, the games are full of weak passive type play to try to hit the jackpot. Outside of that, I pretty much avoid grump central. The freeroll rooms like Flamingo, Ballys, Harrahs can all have some fall asleep games almost on the regular. So if you just want to build up some hours of getting comfortable with the play and pace of NL compared to LHE, those are solid ideas. When Venetian does its daily high hand promo, another great time to find the weak passive play in 1/2. I think the next one isn't until October tho.
Full disclosure, I have played probably 3000 hours of LHE in Arizona and Vegas combined over the last decade, and I have probably about 5000 hours of live 1/2 and 1/3 in Las Vegas (and 2/3 spread limit Arizona) in the last 10 years, so I've seen it all. I have several of the early years of my live poker that I never actually tracked or journaled anything, so those numbers could even be much higher tbh.
Another caveat to 1/2, is time of day. The later the hours of the day/night, the more action games exist, and less of the weak passive type games they will be. These will be the higher income earning sort of game you want to work your way into playing more often than not, but they will be very different from the daytime nit limp small pot games you might be more looking for to tune up your NL play. I would say work your way into them as you feel more comfortable, and if/when you can withstand some bigger swings in your bankroll.
Best of luck on your adventure!