Microsoft has recently released SPFx 1.15.1 Preview version adding a few new features and updates for building SPFx-based solutions. We can find full release notes at the link. With this release we can customize complete SharePoint list form using. SPFx full blog with example.
https://www.c-sharpcorner.com/article/spfx-form-customizer-extension-to-customize-sharepoint-neweditdisplay-form-of/
