Your question is not about "managing your manager." This is about your manager trying to sabotage your career.
Give the talks, quit if you have to. You don't need a manager who is not your advocate. I say this as someone responsible for many more management functions in tech than a technical tasks now. If your manager doesn't help you, tell HIS manager and be open: you don't need to accept this.
Bad management is a poison. Selfish managers need to be lanced out of a company like the malignant boils that they are. Take advantage of a seller's market for technical skills while you can, because there is no promise that you'll have this kind of agency in a year.
I agree that you should seek out a manager that wants to help you advance in your career, but you don't have enough context to judge the manager in this particular case. Perhaps OP is spending too much time speaking at conferences and not hitting his other agreed objectives. Perhaps there is a critical project launch that OP is leading during the timeframe of the conference and it's just not feasible in this isolated instance. Etc.
None of that is material to the judgement here. The fact that the disconnect exists as it stands is evidence of a total breakdown in the manager-associate relationship.
You asserted, without evidence and in absolute terms, that the manager is trying to "sabotage" OP's career, advocated that he quit his job, and that the manager is "bad" and "selfish." That's a lot of assumptions based on four short sentences.
All we really know is 1) OP wants to give a talk at an industry event and 2) his manager asked him not to.
Yes, there seems to be a disconnect—on the OP's side. There may be one on the manager's side also; we don't know. It is also not the responsibility of the manager alone to make the relationship work. People have their own interpretation of events, and ultimately none of us commenting knows what efforts the manager has made and what OP's interpretation of those efforts was.
Give the talks, quit if you have to. You don't need a manager who is not your advocate. I say this as someone responsible for many more management functions in tech than a technical tasks now. If your manager doesn't help you, tell HIS manager and be open: you don't need to accept this.
Bad management is a poison. Selfish managers need to be lanced out of a company like the malignant boils that they are. Take advantage of a seller's market for technical skills while you can, because there is no promise that you'll have this kind of agency in a year.