I think people can overthink it when it comes to subs. Rather than worrying about what specific way to do subs I would say it’s better to understand what you’re aiming for in the end. You can use lowpassed square, or a triangle wave. You can also use sines, in which case I would add some saturation of some sort (I put at least a couple dBs of drive on basically any sub sound with something like the Ableton Saturator or Fabfilter Saturn, smth that can do SUBTLE saturation.) FM synths like Ableton’s operator are great for subs too because again mostly sine wave based but you can bring in some subtler harmonics from the modulators. In the end the important part is more the envelope shaping, note placement, and I would recommend committing them to audio so you can fine edit/fade your sub hits. So knowing your synthesis and putting the time in to clean up and edit your stuff precisely is more important than which technique imo, as long as the fundamental frequency is in that range of ~40-80hz or so (and you don’t do anything weird like destroy it with distortion ofc) it will have enough weight.
As far as questions like “what shape should I make my envelope(s)” and that sort of thing, it depends on the style of track. If you’re just trying to make a sub to match your mid range bassline stuff, try to get it to imitate/complement the impact of your mids. Don’t leave long release tails unless you specifically want a sound that obviously fades out. Most of what I make is more sub-focused than mids-focused so I may be biased. But play around with it, get creative, try reversing hits and stuff like that (another reason to bounce to audio, lets you try things you wouldn’t be able to with a MIDI track). There’s not a lot of right or wrong answers as long as it’s mono (don’t use stereo fx for example) and it’s at a reasonable level. You probably need it a little less loud than you think. That’s my thoughts anyway