A few people are showing interest in this, and while the info is out there, its very confusing so I thought I'd give it the DF overview, based on my somewhat limited knowledge having only just hacked mine as of yesterday
Which models can be hacked?
Boot into recovery mode (RCM)Firstly, Only older models can be hacked, if you bought one within the first 8 months since its release, you should be ok, but, check on that.
The version of the firmware on the machine should be your next port of call, although at the time of writing the current latest version (6.2) is hackable and offers no real downsides over sticking on lower firmwares. If you have a hackable switch and its not on 6.2 already, it's recommended to update now, as it's thought that 6.3 could be a lot more difficult to hack.
Now if you're on 6.2 (or lower), the basic overview is that you'll need to run a payload (software in the form of a custom firmware, which can run homebrew software, this includes emulators, themes, homebrew games and of course, loaders for commercial games).
Loading the payload, aka Custom firmware, aka CFWTo do this you need an RCM jig, which basically shorts 2 pins on the connector on the right hand side of the switch, where the right joycon usually connects. They are easily found and products like the TX SX come with one anyway, or you can jam a paperclip in there if you're feeling adventurous.
Once the console is in RCM mode, you need to send the payload via USB
Which CFW?This can be done a few different ways, the cheapest being by just using free PC software and a standard USB C cable. The problem with this that the CFW, once on your system, isn't permanent and should you hard reset or your battery die, you need to hook up to a PC and do it again.
Slightly more convenient and also free, you can do the same thing using an android phone.
The most convenient method by far is to use a dongle, like the TX SX dongle, which also comes with its on exclusive CFW if you buy the pro version, but there are cheaper variations of these which can do the same thing, albeit with a few more hoops to jump though.
If you hack your system and go online in any way, expect a ban, its that simple. Some people seem to be managing some online activity, but its a slippery slope so if you want to play online, don't hack your switch.Once you are familiar with how this works, you have a bunch of options on which CFW to use, with the main ones being reiNX, atmosphere and the SX OS (which comes with the SX pro dongle)
At the time of writing, Atmosphere and reiNX are working on 6.2, with an SX OS update due any time.
My experience of using these is limited to reiNX, but my understanding is that the main difference between reiNX and atmosphere is that reiNX is slightly simpler, but only accepts commercial roms in .NSP format, where as Atmosphere and SX OS can both accept .NSP and the other format .XCI, although I believe .XCI need some conversion doing to them. It is possible to convert between the 2 formats on your PC, but upon trying I failed and gave up.
This is in no way a tutorial, youtube has plenty of those as well as the main console hack1ng forums.
This post is only intended to give you the basics, you will need to do a bit of google legwork but I can probably answer questions on the info above.
As always, links to ROM files, or anything which may contain copyrighted code and NOT ALLOWED on DF, discussion however is fine.