It depends on the content of the prayers. If the prayers are of a general nature, relying on the values that Protestants and Catholics have in common, then it seems a fine thing to do. But if the content of the prayers are at all uncomfortable or confusing to you, then you could pray your own prayers silently.
I’m not familiar with Seventh Day Adventists but I know I pray with my Baptist and Methodist friends a lot when I go to events at their churches, but a lot of times I find myself “filtering” the prayers in my head kind of haha. If what they’re praying doesn’t have any doctrinal errors than yeah it’s perfectly fine to pray with them. We’re just not supposed to respond to “altar calls” or receive their “communion” or if they profess a creed, I don’t think we’re supposed to say it with them(I might be wrong about the last one though)
There is no rule against it, but the SDA is pretty anti-Catholic. I would be very secure in your Catholic faith and make sure that your friends know that your presence there is as a friend, and not a challenge for conversion. It wouldn’t hurt to have them come and pray with you sometime.
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