You already spoke with Kinsta and got them to enable New Relic? Did that highlight any significant bottlenecks?
The performance issue shouldn’t be coming from the theme itself. It will likely be a plugin you’re using or something wrong on the server-side of things. Unfortunately, it’s impossible for me to tell by just looking at your website/GTMetrix.
I’m afraid I don’t know – you’ll need to work with Kinsta to see if there’s something server-related going on. It’s not something we can debug from the frontend, unfortunately.