Thank you for your suggestion. I´m not sure if I understand what you meam by "Try changing the default behaviour for selecting open office in the windows.", because, as I said, I´ve checked that open office is the default application to handle the ".odt" extension. Is there any other behaviour to change? By the way, I´m using Windows 10 Pro, R version 3.6.3, RStudio Version 1.1.463, Rmarkdown version 2.3, knitr version 1.29. Here is a sample .Rmd:
title: "Untitled"
author: "Your Name"
date: "12 de setembro de 2020"
output:
odt_document
knitr::opts_chunk$set(echo = TRUE)
R Markdown
Although this file knits correctly to ".odt", it opens, for previewing,
in MS Word. I would expect it to preview in Open Office. What am I missing?