Shiny Error, Input HTML must be a character vector of length 1

Hello everyone,

I have difficulties in running the shinyApp. I could not run simplest examples at all.
Here is my input:

library(shiny)
ui <- fluidPage(
  "Hello, world!"
)
server <- function(input, output, session) {
}
shinyApp(ui, server)

And the error message:

Listening on http://127.0.0.1:4994
Warning: Error in htmlTemplate: Input HTML must be a character vector of length 1
  [No stack trace available]

Should anyone help me with this, I would really appreciate it.

The code works for me without issues. with both shiny 1.6.0 and 1.4.0
Perhaps your session got in a bad state, restart and try again ?