What does donation does for open source? Surely it wont come close to pay talented developers who create it. For cloud cost, there are few companies already giving generous free tier for open source.
The only thing that donation could pay for is marketing e.g. events and meetups.
It obviously depends on the project and the scale and duration of a donation, but plenty of open source projects have benefited from donations. Donations can and do pay for developers, as well, part time or full time. With LibreOffice, you can answer your questions directly by browsing https://www.libreoffice.org/donate/ and as a non-profit you can easily find more detailed reports: https://www.documentfoundation.org/financials-and-reports/
That's not true at all. Donations are the biggest source of income for The Document Foundation, the non-profit behind LibreOffice, and have been used to pay developers who've joined the team in recent years:
* Michael Weghorn (accessibility)
* Jonathan Clark (language and scripting support)
* Neil Roberts (scripting improvements)
* Dan Williams (macOS support and general UI improvements)