If I type my credentials incorrectly but really focus on each key press... the service will not accept the login... because the credentials are wrong.

Impressive.

Please actually explain your idea. Nobody is interested in trying to figure out what you're thinking

What they can do, and do do, is collect and read metadata. This metadata will contain info like who you're messaging, when you message, whether you call or text, probably contains approximate or precise geolocation data.

All of this data in aggregate is content by itself.

Facebook don't really care what is in your messages, they can infer all sorts of things from metadata that is useful for advertising.

As an example: 2 people in different parts of the city exchange messages and calls through the day for several years. Then one day, their locations converge in a single new place most of the time and the number of exchanged messages drops significantly. You can probably infer here that the 2 people are a couple and have moved in together. They are likely to want new furniture and the likes and so they will likely see lots of furniture adverts. I wouldn't be surprised if they also saw adverts for childcare , baby things, insurance etc.

You really don't *know* this.

The app is not open source so they can send anything they want to their servers --- including the decryption key.

Any executable connecting with Facebook has the potential to facilitate privacy invasion in any number of different ways.

https://www.theregister.com/2022/02/17/chrome_meta_token/