Ugh, I feel like this might be a controversial take and it's been on my mind lately. How I see it is kinda how you see it too. I don't mind that he donated money to whatever party he likes or supports. However, it got me thinking as well, I should not be paying for a service that potentially might fund his actions and donations in the future, if he chooses to, with money that I am paying for.
With that being said, I support their overall mission to uncensor the internet and give privacy to the people while being free, but I don't want to spend $5/mo if it goes to something I don't support. I'll stop using the browser too and move on to something else as there's a wide variety/alternatives to it.
(P.S. I was already thinking of going to MullvadVPN bc it's the most cheaper option, but I decided against it and would go for Obscura for $3 more after my other VPN subscription expires.)