The thing is Apple and Facebook aren't even competitors. One is a hardware company with software and services on top. The other is a pure internet social networking company (Facebook with feed, instagram for pictures and copying others (tik tok, Snap) and Whatsapp/Messenger for messaging in EU/Asia and US).
Facebook's services run on top of Apple, not in competition with.
For the reason you state, Apple doesn't really see Facebook as a competitor (yet), but Facebook most certainly sees Apple as a competitor.
In the immediate term, Facebook's entire business model and reason for existing is to extract as much personal information as technologically possible from its users then sell it and also abuse it to increase addiction to their products. Apple has made part of its business platform not letting companies do that--making it harder for them to harvest information from you and about your behavior, and encouraging users ever more strongly to reduce the amount of notifications that pointlessly monopolize their attention.
And since Facebook runs on top of Apple, Apple's vision of computing interaction--private and not incessant--is an existential attack on Facebook. Everything that makes Facebook profitable, addictive, and evil is what Apple is trying to hamstring.
In the longer term, Meta/Facebook absolutely wants them to be competitors--Meta's "live life with your VR headset on" vision for the future cuts Apple out of the picture entirely and replaces it with the OS the Occulus hardware uses, and eventually replaces even the open web with a Metaverse they have complete control over.
Taken to its logical conclusion, in the Meta future (and Zuckerberg's most lurid data-harvesting fantasy), they own everything--the hardware, the OS, and even the means of interacting with the rest of the world.
I love how Zuck thinks he's some giant tech genius. He got lucky with a product and is now trying to sell an ad/microtransaction riddled version of a hell that countless cyberpunk novels, sci-fi authors, and computer scientists predicted long before.
To be fair to Zuckerberg, he got lucky with a product, but his real skill--which I'm not sure he has the self-awareness to realize as such--is designing, marketing, and continuing to aggressively push what is essentially a highly addictive, generally harmful, legal drug that doesn't require intake of any chemicals. He frames it as "more connected = good" but what he's really selling is "more addicted = profit", whatever the cost to society.