'Church' these days has been turned into a show by many in the religious world. Worship is for them a big production that is performance oriented and entertainment driven. Such assemblies beg for applause and they get plenty of it. It seems to me that it is a lot of hype with very little of God in any of this.
But getting back to the question about applauding at a baptism, or some good news announced among God's people, I think it a completely different issue, totally unrelated to the above.
For example, should someone be condemned or corrected if they jumped for joy or raised their hands in the air in thanksgiving and praise at seeing a lost soul buried with his Lord in baptism? Would God be upset if someone shouted out loud or danced in the aisles of the church building with excitement because someone He knows intimately repented and was baptized into His Son? Personally, I believe I would be much more concerned if I were not compelled to openly express joy on such occasions. Maybe we just don't get what's happening.
Solomon said there were times when we should laugh, dance, embrace and love, Ecclesiastes 3:1-8. Jesus said there was joy in heaven, even in the presence of the angels of God over a sinner who repents. Luke 15:7 & 10. He told us of a father who celebrated by throwing a big party when his lost son came home. Jesus' apostle Paul later taught us to rejoice with those who rejoice, Romans 12:15. So yes, I believe it is ok to applaud at a baptism.
Life is a struggle in this world. We share our joys and our sorrows when we get together because Jesus taught us that this is how Godly people do it. We sometimes audibly groan together at bad news announced among us and we clap together when good things are announced. If such is a departure from truth and anti-scriptural then I‟ve missed something somewhere.
I have always opposed applause in worship. I will never oppose any reasonable expression of joy in response to good news among God's people.