Still happening as of Nov 6 on iPhone: in dark mode, a reload shows a white page for a split second before the dark theme kicks in.
Same issue as thread-20261027143138-9b45e7f8. The lead in the reply there still checks out against today's HTML: fetching / with theme-hint=dark, the inline critical CSS still says color-scheme: light and --page-bg: #ffffff, with no dark variant. The head script picks the right theme, but those light values can paint first. Generating the critical colors from the resolved theme (or adding a prefers-color-scheme: dark block to the critical CSS) should close it.