Ask HN: Am I dead meat already?

Hi. I've been in the profession (SW Eng) for about 18 yrs now. A few years from my 50s. Didn't go the managerial route. Stayed technical. My current gig is in a very difficult and complex project written in C. Been there for 2 yrs now and I'm afraid that due to the ancient tech stack and despite being a good engineer I'm loosing my marketability.

After enduring bad behavior for nth time (yeah it's a toxic workplace) I decided I had enough and did a round of applications. Mostly for backend positions and mostly for golang positions. I don't have prod xp with golang but it's close to C and every time I've used it it seemed ok. But the problem is that I'm either being ignored or skipped over. All jobs are for seniors in the _specific_tech_stack_. Other positions I've applied for and got no response whatsoever are architects, tech managers and the like. Granded, this regards a turd job market (EU/Greece) but still that's where I am at.

Am I toasted for good? I mean, nearing my 50s with my most recent gig writing "C" on it is as good as declaring my career over?