I think the best thing you can do to reduce stress is practice performing as much as you can. Playing in concerts (solo/chamber), performing for friends/parents/teacher, playing in front of the camera, playing in competitions/masterclasses - all these can help you to get used to performing and tame your nerves. I hope this helps.
Unfortunately, our brains have not kept pace with "modernity".
Back when I had a teacher a few decades ago now, she helped prepared my performances, even arranged to have me appear in some instances. One piece of advice she gave me was practice to your top level, perform at less than 100%.
I normally get slightly nervous before performances, but I focus on the fact that I'm getting an opportunity to share my music with people. Often as pianists, we must work in isolation, so I find it very rewarding to get to share with others the music I have worked so hard on. This thought helps with the nerves a little. Nerves are always there though, but they are normal. Knowing that they are normal is good.
My teacher for a private service was wonderful. She always had voluntary monthly work shops. The adult work shop as I recall was on a Wed night, I so looked forward to them. Maybe 10 or 12 of us showed up every month. We had to play if you went, show our wares sort to speak. This was my sounding board and it gave a reason to prepare work and just up it a notch as well. I remember some people being so nervous their fingers were shaking over the keys but most of them still showed up. But this kind of experience is priceless if a person has goals to play out, IMO.