What is the best free Office software for general odds and sods (mostly using Word, sometimes simple spreadsheets)?
Libre Office, Open Office, Free Office?

I tried Office 365 online - it's great but I want to be able to click on a file anywhere on my computer, and not have to upload it to onedrive first.

Thanking you.

vim + latex

Or you could try LibreOffice

Latex all D way

If you don't wanna pay you are kinda fucked. LibreOffice is the better choice but it is so far behind on the features and UX that I just pay for Microsoft Office.
If you dont do any professional work LibreOffice will be just fine, the last time I opened OpenOffice it crashed my entire PC but that is ages ago and probably fixed, I haven't tried since.
Don't listen to the vim+latex crowd, it's the same as tarkov players, they just want to spread the suffering

there's also markdown. dunno if that counts, I have no opinion yet on the subject