Yes. There is evidence that Google and Facebook have monopoly power. Google has 80-90% market share in search and Facebook has similar market share in social media ads. Network externalities make it hard to compete with them.

You can also make case about collusion between FB and Google emerging around 2010-2013. They have divided the markets and have stopped competing. It's hard to find evidence that it's intentional. It can be just understanding emerging from single meeting or natural development. Whatever the reason they seem to avoid direct competition.