I often confuse the two phrases.
My Google search for them has shown that the use of "tens of thousands of people" is overwhelmingly popular compared to "tens of thousands people".
Based on the search result, I first thought that the use of "tens of thousands people" was wrong, but later found a BBC news article employing the two similar phrases in it as below.
An unprecedented economic crisis in Lebanon has pushed tens of thousands people into poverty and triggered the largest anti-government protests the country has seen in more than a decade.
Tens of thousands of Lebanese took to the streets, leading to the resignation of of Western-backed Prime Minister Saad Hariri and his unity government.
Are both phrases just interchangeable? If there is any difference between them?