WinForms did not even support dark mode until .NET 9. Before that I was literally using an open source library some guy who works in Antartica wrote during his downtime, probably to keep from going nuts, lol.
Historically I have done line of business apps for a living and theming or skinning has just never been on any of my client's radar. However, a general release app would definitely find it invaluable. Or who knows, I may acquire a new client with taste!