But usually commercial use means “if a company is mandating it be used”
That is wrong. Commercial use is a very clearly defined legal term.
Source: I work in software asset management and you wouldn’t believe the insane and sometimes malicious licensing models that actually exist, while you complain about and blow up this very benign issue.
What is the difference between me, one dude at my company, taking personal notes via obsidian, and some freelance developer using it in their business? Why does the number of people working at my employer make my use commercial?
If you are a freelancer, then you have to pay for all of your expenses yourself. The devs are in a similar situation and they know how hard it is, to keep yourself afloat, when software licenses are sometimes incredibly expensive.
If you are working in a company with two or more employees, then your employer has to provide and pay for any commercially used licenses that you require for your work.
If you are using Obsidian for work and consider getting a license, request it from your employer, explain how it would improve your workflow, save you time, etc. If your employer rejects your application, then you must stick to using the software that your employer provides you with. If that is MS Word, then your employer mandates you to use MS Word (or pen and paper) for note-taking.
Second brain inevitably includes work-related stuff. So, no, not free for that use, right?
Are work and private life not separate areas of life? Which would belong in separate vaults? And does your employer not provide you with a separate computer for work? Are you using your personal computer for work or are you using your work computer for personal stuff? If it’s the former you almost sound like a freelancer, if it’s the latter, then you shouldn’t do that.
If you just write about work in your diary notes or hold onto an idea for work that you got while grocery shopping, then this is not work use and you are fine, but if you attend a work meeting and take notes using Obsidian, then this is clearly commercial use.
There really is no magic to it. It’s not complicated or broad (quite the opposite actually). In the end, you can do what you want, but don’t frame indie developers as ‘scummy’ for trying to make a living, while you profit off of their work. With this I will now end this conversation.