For another anecdata point, https://analytics.usa.gov tracks user device demographics to all visitors of U.S. government websites. Which of course might skew in ways different than the general U.S. population. But checking out the numbers right now for Linux users:

Last 30 days: 6%

2025 so far: 5.7%

2024: 4.5%

edit: analytics.usa.gov includes iOS and Android in its operating systems breakdown — e.g. Windows has a 32% share vs OP's 63%. Assuming most of Linux users are on desktop, it could be the case that Linux share in desktop users is a bit higher than 6%