I think the issue was, that I need to install via github to get the latest version (4.7.1.9000). Seems to work, but I get this error message (using the examples):
You’ll need the dev version 4.7.1.900 - install with devtools::install_github("ropensci/plotly")
Plotly’s latest CRAN release 4.7.1 uses an older version of plotly.js (v1.29.2). Whereas, scatterpolar trace type were added in plotly.js v1.33.0. The dev version (4.7.1.900) of the R package uses the latest plotly.js release (v1.35.2)