There’s no calendar for my country, but I added the calendar from officeholidays.com a while ago. I’ll have to keep using it.

And they will continue to do it for a while, for the ESR version

OnlyOffice Docs is a web office service, but this is a new release of OnlyOffice Desktop Editors, an offline version, available for Windows, Mac and Linux.

If you have the knowledge or want to learn about it, and you are willing to deal with these tasks (configuring the system and keep it updated), the DIY approach makes sense.

I was on that situation some months ago, and I didn’t want to spend time in system maintenance, so I bought a NAS device.