R maps look bad in RStudio Plots pane but work when exported

Question

I am using the tmap package in R to create a series of choropleth maps. As I am following an online tutorial, I know what the final maps should look like. However, when I try to visualise the maps in the RStudio Plots pane, the proportions, positions, and text sizes look very different to how they should, and the map itself doesn't look good. Yet when I export the same map with tm_save(), the proportions work again and it looks like how it did in the tutorial. This works without even having to specify plot size. This is frustrating because it means that I can't use the RStudio Plots pane to refine my map design, and instead have to constantly export my maps to check how they look.

I have a similar problem with RMarkdown: the maps look untidy when generated in the RMarkdown document, but when I export it as an html file, the maps look good again. The proportions also don't work when I use the windows() popup.

I have already tried setting a default size for my Plots pane, have reinstalled tmap, and have searched StackOverflow for more advice, but can't find people with the same problem as me. My RStudio is already on the latest version.