Socialism has to to with collective ownership of the means of production and distribution of goods, not cost to the consumer. Goods and services may typically be free at the time of use (funded by taxes ahead of time) but that does NOT mean free as in without cost.
Again, like most of the other people in this thread, you’re confusing free as in freedom (software movement), and free as in without cost.
I agree that socialism is not the scary term that staunch capitalists seem to believe that it is. However, perpetuating misunderstandings about what socialism means will not help find a healthy balance.
Others are recommending Obsidian (which I have no experience with, it may be the right way to go).
Myself, I chose Logseq on a whim a year or two ago and haven’t looked back. In the backend you get a nicely composed set of plain-ol’ markdown files that you can cp/edit/merge as needed.