Now I know this may sound like a really dumb question but the reason I want to know is because I want to be able to buy Doom 3 on Nintendo switch but I can't because I am 17 and it requires you to be 18+ in order to play. I watched a video that showed you can make a separate account for your switch and make the age 18+ and than you can buy the game on that account and play it through your main account. But I'm worried that the game will think it is owned by the second account and not the main one which would be a pain because I hate having multiple accounts with different games on them. So I was just wondering If my main account actually would own Doom 3 if I buy it (they both use a different email)
I'm worried that the game will think it is owned by the second account and not the main one which would be a pain because I hate having multiple accounts with different games on them.
The game will definitely belong to the second account. I know this because my wife and I have two separate accounts on the same Switch. An account can be linked to multiple Switches, but only one Switch can be identified as the "primary device" for a given account.
Games bought for a given account account are:
visible in the installed games list for all accounts on the device.
playable by all accounts on the device if this is the primary device for the account that owns the game.
playable only by the account that owns the game if this is not the primary device. (And you will need an internet connection at all times.)
available to be downloaded from the eShop only by the account that bought it.
Here's some more detailed information about primary device vs non-primary device.
I wasn't able to find any information on whether parental controls would block your first (under 18) account from playing the game bought by the secondary (over 18) account. You mention a video that shows you how to do this and that it works, but I find that a surprising oversight on Nintendo's part. Be aware that even if it works today, it might get patched out tomorrow, and that would presumably lock you out of any saves for that game which you've built up on the first account.
Also, be aware that once you have multiple accounts on a single Switch, it will pop up and ask you which account you want to play with for every game on that Switch, regardless of which account owns it. Which means if your parents ever use the device themselves, they may notice a new account they don't remember creating in that list.
I believe a list of accounts associated to the device is also available through the parental controls app on iOS (and presumably Android? I have an iPhone.) I haven't played too much with that, though.
If the accounts are on the same switch, yes, you can play it on your main account (on that switch) but the game will be owned to the other account although I cannot see why this would be a problem unless you owned another switch. If you were to log in on your main account on another switch, you would not be able to play doom unless another account on that switch had doom (eg. Your other account).
As Steve-O's answer details, a game that you purchase on a second account will belong to that separate account - as far as Nintendo is concerned, the second account, with a separate email, is an entirely different person with their own wallet and own set of purchased games, and the two accounts can only share games using Nintendo's limited device ownership rules.
However, there does exist a compelling reason to do this despite these rules: regional accounts. Quite a few players (usually enthusiasts) in North America or Europe will create a Japanese account in addition to their home account in order to play games that only release in Japan, or that release in Japan first and in their localized region later. The different languages' copies belong to separate accounts, of course, but as long as you only use the alternate region account for games that need it, it shouldn't be much of an issue.
This can be helpful in your case because it also affects ratings and parental control limits. While Doom 3 is rated PEGI 18 in Europe, it is only rated M for Mature in North America, which places an age restriction of 17+. Therefore, you could potentially play Doom 3 by creating a North American account and purchasing it through there.