If you're in the same company for 3 years, it usually means it's time to move on. Boredom, a fear of stagnating skillset and increasing your income (and those reasons are not in any particular order) are the main reason why software engineers change jobs every 18 months to 2 years.
Tell your recruiter
I am the go-to technical expert on my company's mission-critical app, responsible to our government customers and their citizens.
When asked why you want to change jobs, say that you're always learning new things and the new job offers you a great way to do that.
Ypu could say the same sort of thing to your current manager, and ...
I would say it depends on what exactly you are doing. Aspects that are likely to hurt your carreer in the context of working only on a single project
This technology is exotic
Project is bound to a single use case at a single customer
The first two are technically oriented. If you do only know one exotic language/...
I am a kind of person who always look for something challenging and I am not getting it.
Question is: what did you do go get something challenging?
Did you talk to your manager about this?
Did you explore the problems that you or your organization may have (other than assigned works) and did any brainstorming to come up with ways to solve them? This can ...
I think it depends where you are
In places where volatility is understood, it might be accepted. I am in Calgary (where oil makes the economy volatile) and I don't know anyone in technology who has stayed in a position for longer than 2 years. They either got a promotion in under 18 months from their company or got it from someone else.
They don't get ...
If it is understood that startups are like this is it also understood
by hiring people that an employment history full of startups is going
to contain a lot of hopping?
They aren't like that and it's not understood to be like that. The 9 out of 10 failures number is uncited and almost certainly plucked out of thin air. Under a year average work span is ...
In the contrary, you should be happy you are not forced to do support and your responsibility lies only in developing a new system. Probably they let you in there so you won't leave running for greener pastures, had they asked you to do support.
In any case, if you see that your skillset has stop expanding with your current role, maybe you should start ...