The end of Windows 10 is approaching, so it's time to consider Linux and LibreOffice
(blog.documentfoundation.org)
A particular version of Linux Mint, the example you mentioned, is supported for 4 years, whereas Windows 10 was supported for 10 years.
True, but often the distributions have an upgrade plan (for free). In example you can install an Ubuntu LTS and upgrade 4 years later to the next major LTS release. However, sometimes this has problems, because so much time and changes are in between. This is for sure.
There are distributions with longer support period. Debian comes to my mind. But I don't know how long and there were 10 year supported distributions too.