None.
X-Plane comes close to FlightGear. It has far-superior visuals. fully functional glass cockpits like the Garmin G1000, and simulated ATC, but the vast array of community-made planes available in FlightGear still kinda seals it for me, despite the jank.
FreeCAD has its pain points. Software like Creo Parametric is much more robust in a lot of ways, but I literally cannot run it on Linux (no mouse-wheel zoom in WINE, slide show in QEMU). Fundamentally, they are similar enough, and my work primarily takes place on a component level so I can live without the streamlined assembly workflow. Also, FreeCAD doesn't cost >$2000, and can still do FEM analysis and computational fluid dynamics. Maybe I could find a crack for SolidWorks and try that out, but it takes a long ass time to learn a CAD system proficiently.
Everyone who learned on Photoshop says the GIMP interface is weird, but I learned on GIMP and can say the same for Photoshop.
Games are the only exception, but games aren't fungible. Minecraft is not a substitute for Dwarf Fortress. CS:GO is not a substitute for Unreal Tournament.
Setting up email is a fuck. Every once in a while I check the mail server for my mastodon instance and there's always sign-up mails which were undeliverable. The server is only on two block-lists and those block-lists block the whole IP range because it is a VPS host. Most providers work, but iCloud and ProtonMail in particular reject everything.