I think your issue is being tracked at reactR/R/dependencies.R: Shinyapps.io deployment fails to load react-tools.umd.cjs provided by dependency reactwidget-2.0.0 · Issue #86 · react-R/reactR (github.com)
You need to revert to reactR 0.5.0 using something like this:
packageurl = "https://cran.r-project.org/src/contrib/Archive/reactR/reactR_0.5.0.tar.gz"
install.packages(packageurl, repos=NULL, type="source")