They might have one official employee but there are a bunch of people active on their github. They might be contractors or employees of a different related company.
Feels like a complex situation to me - I like that there's all sort of software out there, esp. if there are improvements to UI/UX, but also I think that the OpenDocument formats are nice to support when possible and push as defaults (while they unfortunately might be a bit confusing to casual users who are used to MS ones).
I tried OnlyOffice and it seemed okay, even if I daily drive LibreOffice most of the time. It's nice that it's open source, but I also understand the people who are cautious about stuff coming out from Russia - I wouldn't hate on software for being developed by people from there, but it also presents an obvious risk.
They might have one official employee but there are a bunch of people active on their github. They might be contractors or employees of a different related company.