Amazon: https://www.cnbc.com/2019/07/17/eu-to-investigate-amazon-ove... & https://www.forbes.com/sites/enriquedans/2020/06/13/if-amazo...
Google: https://finance.yahoo.com/news/google-sued-again-over-anti-0... & https://www.msn.com/en-us/news/technology/anti-competitive-g...
Facebook: https://medium.com/swlh/facebook-is-killing-the-competition-... & https://thehill.com/policy/technology/529504-state-ags-ftc-s...
Granted these are just lawsuits at the moment and not final verdicts but still it's not hard to see how they don't play a fair game.
For a monopoly, you need anticompetitive practices. Is Facebook unfairly preventing the success of other social networks? A good example of a monopoly was 90's era Microsoft, which prevented its OEMs from shipping competing operating systems.
Terminology aside, I completely agree with you that we need far, far more choice in the marketplace.