Embrace. The big corporate giant dips its toe into an existing project.
Extend. The corp adds features to their app, improving on the community’s apps features. Somewhere along the line, a previously open source project will become proprietary and closed. People begin to prefer the proprietary option for the added features.
Extinguish. The proprietary app cuts out the original community (defederation) when a critical mass of users is reached. People use the proprietary app instead of the open and free app, because of the features, but also because many of the people they want to follow are now segmented from them. The original open system dies out from lack of use.
Enshittification follows.
Companies should be required to pay if they take the software, modify or fork it, and then sell it to others. That’s the only case in which I think anyone should be paying for libre software.
For example, the linux kernel is used by android. Google modifies the kernel source and sells it to phone manufacturers. Linus Torvalds (and the rest of all kernel devs) deserve a stipend for the use of their work to generate profit. Also, the modifications should be legally required to be open sourced if they don’t pay.