If a good percentage of your Obsidian usage is directly work-related (e.g. you frequently need to look up things in your vault in order to do your work), a commercial license is needed.
We understand that it’s often not easy to separate work and personal, and if you use Obsidian to document your learning or knowledge, those bits of information would inevitably be applied to your work. It’s okay to do that without a commercial license, but for example if you constantly use Obsidian to take meeting notes during work or store a team knowledge base, that would require a commercial license.
Not a super clear line, I agree, so please use your best judgement. We trust your judgement!