I know people who became a PM assuming the PM has the power to make the decisions. BUT you need to work with the CTO to create the vision, validate demand, get you idea, work with marketing to announce it, identify design partner customers, work with designers and work with Engineers to agree on the MVP, oversee delivery, get the docs written, get support trained, run the early access program, enable the field, and finally work with marketing to the release your product. AND - by the way - none of these people report to you. How do you do it? Politics are unavoidable.
And let’s say you do all these things exceptionally well — guess what? Nobody will ever be satisfied with the decisions and tradeoffs you made. When things go wrong you will get blamed, and when things go well sales makes the bonus and Engineers are praised. There will be long stretches where you wonder if it’s all worth it.
BUT there is nothing like delivering something customers love and it makes it all seem worth it. Hang in there. :-)