Learn LaTeX and then come back here. Or better yet, learn LaTeX, write some documents, wait 10 years, then come back after revisiting those documents.
I think I first started learning LaTeX in 2007 or 2008. I began writing HTML around 1995. IMO, anything resembling a "document" that you expect to be useful longer than a year or two should be written in LaTeX, or at least something based directly on TeX. Alternatively, just use plain text. Anything else just doesn't have a comparable shelf-life.
Whether it was intended to render to screen or print is totally irrelevant. If anything, stay away from screen-oriented formats because there hasn't been a standard "screen" format like, ever, with the possible exception of TTY geometries.
And output format isn't even the half of the relevant qualities to worry about when it comes to shelf-life. TeX is basically written in Pascal. TeX is a standard as well as its own future-proof implementation, permitting pixel-perfect reproduction across decades. I expect direct ports of TeX to Web Assembly not long after the standard sees adoption.
Of course, TeX is not the same thing as PDF; not even remotely. But TeX is oriented toward the world of hard copies, and I hardly see that as a fault. But even if so, it's de minimis in the grand scheme of things.
Actually, 99% of written materials might be perfectly readable (on a computer screen) in plain text format. For them even HTML is an overkill. A good reader app will let you choose the RX ("reader's experience"), but even a simple text viewer/editor would do the job most of the time.
