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You should at least play around with the export options and do regular exports. You really don’t want your diary of over 5 years to be stuck in an unmaintained app. And since this seems to be supporting exporting into markdown - maybe try an export and checkout logseq or Obsidian?
There are better gadgets to track your sleep. If you want to just track how you’re sleeping, get a cheap fitbit. Withings or Apple Watch are also able to detect sleep apnea