"countless of times" is a correct and usable phrase in written English. You can use it to refer to an extremely high quantity of something, for example, "I have told you countless of times to be careful."
This is nothing new, written about countless of times.
"What's happening with 'The Contender,' they've done this countless of times".
City Mapper is a lifesaver and has saved me countless of times.
Its elements and style have been used countless of times in other works and many analogues of the cynical John Constantine have appeared.
The fear of public speaking has been nominated countless of times as the most popular fear more than the fear of death, heights, and snakes.
I have been told that countless of times and I just tell them that I'm a 36-year old woman trapped in an 18-year-old body.
We had tried countless of time to put all of my eggs in my one basket... but it just wasn't working.
The history between Ponting and Harbhajan had been somewhat akin to that of the Israelis and the Palestinians, both having clashed countless number of times with mutually-directed verbal barbs.
Look at all the paper and trees, he said, that could have been saved if people had not had to write or type out those slashes on paper over the years -- not to mention the human labor and time spent typing those two keystrokes countless millions of times in browser address boxes.
Consider the countless number of times that your cells divide to make you who you are.
Every particle smacks into another countless trillions of times per microsecond, all moving at the speed of light.
Since I tried Ludwig back in 2017, I have been constantly using it in both editing and translation. Ever since, I suggest it to my translators at ProSciEditing.
Justyna Jupowicz-Kozak
CEO of Professional Science Editing for Scientists @ prosciediting.com