Here is a two-step solution hopefully:
1. Convert the numeric value into an integer
2. Create a text string with the integer in it.
Here is the little test:

One start variable: a numeric input with the value 4321.56

followed by:

I added the '<' and the '>' just for clarity in the output here.

Gives the result :

Thank you, @WouterT
The 2 step process worked.
It didn't occur to me to use the operation "Create a text string". I was originally using the action "Format number to string" and it added the comma thousands separator as well as the ".0" at the end.
I also tried skipping the "Convert a value" step, which converts the number to an integer. And that produced a string without the thousands separator, but the ".0" was still displayed.
So, the 2 step process is the winner. Thank you!