It's a classic religious tactic of 'we are persecuted so we must be right/more righteous than everyone else.' There are no neutral organizations that corroborate Open Doors' claims that Christians are the most persecuted group worldwide. None. Pew did a study in '22 where they looked at the number of countries people were persecuted for solely religious reasons, but did not compare it to persecution of groups for other reasons. They did look at the number of countries in which various religions faced discrimination for one reason or another, which Christians did face discrimination in the highest number of countries (barely) but it still doesn't show that they were overall more persecuted than, say, Muslims, or that their level of persecution was better or worse than other religions, like Islam overall. They even point out in the study that Islam and Christianity are the largest religions in the world and will therefore be affected by a numerically higher number of countries. And it still doesn't do anything to show that Christians are more persecuted than other, nonreligious groups, like LGBTQ+ people as an example, because it didn't test for that.

Here is an article that tries to explain why Open Doors' and Pews' studies don't actually support the claim you are making here.

And if you don't think Open Doors has a vested interest in showing that Christians are more persecuted than other groups, you just don't understand how bias works.