You can do something like this:
---
title: "MWE"
author: "Raniere Silva"
date: "08/11/2021"
output: html_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```
```{r}
`foo bar` <- 1
```
'foo bar' is `r get("foo bar")`.
This obviously a rich incentive to not use spaces in variable names. If they occur in data files, then they should really be repaired using (for example) janitor::clean_names().
Stephen