This article might provide some insight:
https://earthly.dev/blog/bazel-build/
My thoughts, as someone who has done a lot of build engineering, but that has only a small amount of experience with bazel:
If you are working with languages that are well supported by existing, maintained bazel rules, maybe. Otherwise, the answer is likely "no". You do not want to take on the burden of maintaining significant rules, or figuring out how to mate your ecosystem of choice to an opinionated build system that nobody else in your ecosystem uses.
If you can manage with something easier to setup, it probably makes sense to do that instead. My general experience in startups is that you have to "pick your battles" constantly. You don't have the luxury of infinite time and resources. Work on the build system has a high opportunity cost.
Most developers and other people who aren't build nerds care about the answer to two questions in regard to builds:
1. Is the build fast enough?
2. Is the build working?
That's it. This is frustrating when they don't understand the other important aspects of build system quality, but it is also, admittedly, somewhat of a pragmatic perspective.
There is much leeway inherent in the speed question. If the build is slow, people can wait. Do they have any other choice? There is plenty of other work to do while they wait.
If the build doesn't work, you, THE build guy, are going to feel the pressure to get it working again quickly. This often turns to bodging, and eventually to something resembling life support. However, nobody will care how much of a brittle, knotted mess the build code is if it still manages to mostly work.
To put it bluntly: A startup company can probably survive with a shit build system. And that might even be the right answer depending on the context.
I would personally be perfectly happy to get paid to set up a beautiful, apex example of a build system for a startup, whether it makes business sense or not. My professional integrity just won't allow me to recommend that path unless I think it's justified.
I might recommend to start with a script, or a makefile, or a ninja generator, and see how that works out first. After all, that is how Google did it for a long time before they decided to create Blaze.