That could be a lot of things. With a laundry room over top you can have a drain line as well as water lines lined up going down through a plumbing wall, as well as electrical. Honestly I hate stud finders personally. You can always take a drill bit or screw and run it in slowly and see if it hits something, if not use the anchors. Or just try to mount where there's nothing in that area. The other option is cut it open and see what's actually there. If you use anchors you can get ones with screws that are short enough to not hit anything after testing the depth with something like a drywall screw or just a small drill bit. Make a mark on the bit or screw so you know the depth that it's going to run in when utilizing the mount and if you don't hit anything in that depth you're good to use it in that location. If you can't find a spot that satisfactory just mounted on a piece of board and move on

Leave out the stand-offs, if your TV is less than 50#'s I wouldn't even bother with the plywood. Mount the bracket with 2 lags into a stud then use heavy drywall anchors rated for 50-100# each into your drywall. The single stud will support the weight while the anchors will help they will serve to prevent sagging downwards. If it's more than 50#, 1/2" plywood is More than enough as a backer, or just grab a 1*6 and cut to needed length. Whatever is cheaper or on hand will suffice. Mount that to studs with some construction screws then use included hardware from TV mount to install centered on the board/plywood. Make sure that the screws going onto your board (if used) have threads in the wood and not smooth shafted when fully installed. If they threads are not towards the head of the screw you won't have any holding strength so in this case just go to the hardware store and get some that will work properly, going into the drywall isn't necessary but won't hurt overall, don't assume it to be structural though (this is why you need threads of screws into the board, not smooth shaft)

Returns

This

Read some more and found it in the NEC that your not supposed to bury it because it's not rated for abrasion/puncture resistance. And for some reason it's not allowed in conduit except in certain circumstances but it didn't clarify where I was reading.

However, it's your property, your land, your risk. I would personally bury it as long as it's not in an area it'll be damaged. I'd possible you could rent a small trencher and bury it inside an oversized conduit (so it pulls through easily).

There's nothing in the code as far as I know stating you CAN'T run Romex or SO in conduit, it's just probably that people assume. "well it fits in this one so it's all good" but you need the airspace for heat if it warms up while being used.

You can run Romex in conduit but you have to size appropriately. Your cord is 10ga/3wire so you need to size for that. You could always just bury the cord if that's easier. It has a rubberized coating on it that is fine for that purpose.

Pulling it 500' through conduits would be an absolute bitch but sure you could spend the time and $ doing that.

Sizing guide

https://www.thespruce.com/number-of-electrical-wires-for-conduit-1152860

It's so cord, it's fine for that use as long as it's not gonna be driven over with like a lawn mower