As others have said journals are pretty neat and actually live on a spectrum where the chronological aspect is the common defining feature. By that I mean you can keep something like a gratitude journal where you write daily a set number of things you are grateful that day (after a bad flu I was grateful to be able to swallow without pain for example) or at the other end you have work journals to keep track of what you've done on that day if you ascribe to the CYA professional principle. For a while I kept a physical bullet journal but at some point I went digital instead.

Generally speaking even the "Dear diary," style of journal is helpful, if not to gather your thoughts and reflect then at least to practice writing.