Is not knowing a "core" language for a senior position more unforgiving than for lower positions (junior and mid levels)?

I'm currently employed, but I'm looking at other jobs and applying because things are not going well at my current company. We’ve had a few rounds of layoffs over the last two years. I survived them a

I'm currently employed, but I'm looking at other jobs and applying because things are not going well at my current company. We’ve had a few rounds of layoffs over the last two years. I survived them all, but I don’t feel comfortable or secure anymore. There are a few other minor issues, but if it weren’t for the financial problems and job security concerns, I probably wouldn’t be looking elsewhere. Anyway, I have experience with several languages and technologies that I’ve learned through all my jobs and side projects. However, there are still plenty of job postings for senior developers requiring experience with XYZ technology that I’m not familiar with. In my case, that’s Java. I just never had to learn it for any project or job. I recently sent a few applications for positions that require Java, but I think I’ll be instantly

rejected because it’s a core technology for those organizations. Do you think this is true? I feel that when you’re applying for junior and mid-level positions, companies are a bit more forgiving if you don’t know their “core” language. Obviously, even senior developers won’t be super familiar with all the technologies listed in job postings, and that’s normal. But now, as a senior, it feels like I’m locked into my current knowledge, and it’s harder to get a job if you’re not familiar with the core stuff. This isn’t an excuse for me not to learn Java (and something like Spring) in my spare time. I am planning to learn as much as possible, create some kind of simple but presentable app, deploy it, and share the code on GitHub. I’ll do that, and in fact, I’m confident that with my current knowledge, I can get onboarded much faster than when I was a junior. But will this be enough for senior Java positions?

Additional context about me: I’ve been a full-stack web developer for about 8 years now. I’ve been at my current job for almost 5 years, and this is also the job where I was promoted to senior. I have solid experience with several languages, as well as working on high-traffic/load applications and scaling them, various databases, working effectively with other people, leading and mentoring etc. My reason for wanting to learn Java is primarily to open up more job opportunities in the future because I want to feel more secure even if my company isn’t doing well or if I don't like my current workplace anymore. P.S. I didn't define "core" language, but from my experience there are companies that only use one backend language, and there are companies that use multiple languages for their backend stuff. For those who only list one language or framework, I call it a "core" language, and it's almost a hard requirement in most cases. On the other hand, my impression is that when a job posting lists multiple languages or frameworks, usually there's no core language that's a hard-requirement to get a job. This is my observation, but I'm sure there are exceptions or more nuances than that.