Unfortunately, as many posters have mentioned here in 2020, the app's development is no longer. I've been successfully using it for years but if you have Big Sur, Dyrii won't launch on it which is hugely disappointing. The developer has abandoned the app and its users without so much as a basic explanation (of course, it may be he met an unfortunate end, so that's something to keep in mind given COVID and the over 1 million infections in India).
I have some solutions that might help others though: First of all, if you are syncing with iCloud, your data should still be there. I didn't realize that you can also sign in via a web app at: https://app.dyrii.com/login and access your info. Also, I'm running it on my iPhone (iOS 14.3) and the app still launches, entries are still there. If you have the desktop app and are running macOS 10.13, 10.14, or 10.15 you can open the app, or copy the app and its data file (if locally stored. If in iCloud, copy from there) from macOS 11 Big Sur to see your entries. I recommend exporting them as soon as possible into a standard format like PDF so you don't lose anything.
I've tried many app. DayOne used to be great before they went to the subscription model and now I'm considering returning to a good old fashioned password locked MS Word file as my journal. Creating one per year can help with archiving so you don't risk too much on one file.
I hope that helps others. Good luck.