That's not true, he donated to organizations supporting California Proposition 8 which banned same-sex marriage which by the way was supported by the majority back then in California. That was also 16 years ago, it's time to let it go and stop spreading misinformation. You should instead not rely on ad-hominem and critize Brave for being ridden with cryptocurrency and doing shady stuff.
And donating to a specific cause shows a lot more commitment and understanding than a typical vote.
2. What does "cancel" even mean in this situation? Calling him a jerk or deciding not to use Brave is definitely not worse than "the most extreme things you could donate towards".
3. There are plenty of things that could be construed as a "political opinion" that are valid targets for criticism and avoiding contact over. In particular, politics are full of scapegoats, and judging someone for participating in scapegoating is entirely fair.