An alternate that was recently presented to me, was a plugin for Chrome and Firefox, created by someone and promoted in the Unofficial Figma Community Discord Server.
From that post: “Hey, colleagues Designers! If one of you works in Figma in a browser, then you are probably experiencing discomfort due to the lack of dark mode. I decided to fix this, and made an extension for Chrome and Firefox that makes Figma dark. At the moment, this is the most worked solution available, and besides, it is absolutely free!”
Install for Chrome:
Install for Firefox:
PS: I did not check this myself, because I do not mind the white… but for all the rest, this may be a nice solution.