I've experienced this as well, even after years of experience. The fundamentals all transfer, but ramping up on an entirely different language/stack/toolchain,

I've experienced this as well, even after years of experience. The fundamentals all transfer, but ramping up on an entirely different language/stack/toolchain, an entirely different business/industry, and an entirely different company culture/management/process all at the same time can be a really big challenge, especially in more senior roles where expectations of autonomy are high. But eventually you finally get over the hurdle and it starts to click. I've done it a few times, and each time I have to remind myself that I've done it before and I can get through it. Fortunately, so much of being an effective senior engineer is not about programming. But it's hard to remind myself of that when I feel like a "bad" programmer in a new stack for a while.