At the end of the day we must remember that people need to make money and most simply don't have the time or desire to make open-source for free. And until more people actually get adequately paid for making open-source, open core should not only be tolerated but encouraged. Because the alternative is open-source projects dying or people just not making open-source at all.
Now there are definitely people and companies that put "open" on things which are not open* (e.g. OpenAI, or any ML company which claims a model is open-source but does not distribute the weights). But if a project has 100% of the code public and an open-source license, the project is "open-source" and the owner can't just take it back. If they try, or try to steer the project in a proprietary direction, the community can fork.
So open-source with paid auxillary services, support and training, and a GPL (maybe not AGPL) license is still open-source and IMO completely fine. Ultimately, the ability to fork and self-host is what differentiates real open-source from fake.
* Because on the other hand, providing a facade of open source is usually also the only way for many to popularize a commercial library. For many reasons, solo developers and businesses don't want to use closed-source binaries. Some other SE projects e.g. languages are like this as well. So we have genuine people just trying to make a living and greedy executives abusing buzzwords both choosing "open core".