I was a Windows dev (now retired) and from the late '90s that's exactly how I kept a daily log: a Notepad file with .LOG as the first line gets date & time appended every time its opened. Notepad used to have a rather small filesize limit, so I'd just make a new file every month or two. Later I used TextPad [0] a commercial Windows editor which also supports the .LOG-as-first-line system, as TextPad can handle arbitrarily long files.

[0] https://www.textpad.com/home