I would love to see the actual numbers there. JetBrains uses Java for Windows/MacOS portability, so the marginal cost of supporting Linux is negligible. I wouldn't be surprised if the actual Linux revenue for them is about 1-5%.
About half of the users of JetBrains Software have a development environment on linux (beating MacOS). And about 60% of the projects that the developers code are being targeted for linux (presumably for Servers, but still a lot)
Source: https://www.jetbrains.com/lp/devecosystem-2020/
Sure, but about 90% of their userbase is happy with the free community edition and will never upgrade. What is more interesting is the distribution of the remaining 10%.
The Humble Bundle used to release actual numbers. For sales that offered games on Linux, Linux users accounted for around 20% of revenue, often beating out Mac. Interestingly enough, for sales that only offer Windows-only games, Linux revenue still reaches 1-5%.