There is only one church. It’s the one Jesus established. As catholics, we understand the catholic church to BE that church.
In the broadest sense, all baptized Christians are of the church. But there are degrees of separation and disruption of the unity that Christ intended there to be in the church. The Eastern Orthodox are of the church, if imperfectly due to refusal to accept meaningful primacy of the Petrine office. More recent schisms also exist within the church while retaining apostolic succession to the extent that such communities can be called “churches.”
Protestant communities aren’t technically called “churches” in official catholic terminology. Instead they are called “ecclesial communities.” The members are often referred to as “separated brethren” in that they are our brothers via baptism (Grace), but tragically separated from us via their rejection of apostolic succession.
In the broadest view, baptized individuals are seen as members of the church, but communities of Christians who have separated themselves from apostolic succession have lost a crucial component of what Jesus intended the word “church” to mean.
Good thing God is merciful or we’d all be in the soup, eh?
Perhaps the family is a good analogy. Imagine a couple has 12 kids. They all grow up and move out on their own. 11 of them marry and have kids of their own. The 12th doesn’t marry and feels a bit left out at family gatherings. As a result, she drifts a bit from regular contact with the other siblings. This doesn’t make her NOT part of the family, but the relationship is damaged. Call her the Eastern Orthodox (don’t read into the kid thing!) Another has a huge knock down drag-out fight with the family father and refuses to attend overall family gatherings if the dad will be there. He still has contact sometimes with the siblings, but never when dad’s around. (He’s the protestant). Everybody fights at times, of course. They’re siblings! In the end, they’ll always be family, whatever comes. But not all family relations are as close as they’re supposed to be.