Hi Jeff_M:
Your screen flash might be related to the bug reported in yomama’s 26-Mar-2025 CCleaner ver 6.34.11482 freezes computer for 10-15 seconds after cleaning finishes.
Dell Inspiron 15 5584 * 64-bit Win 10 Pro v22H2 build 19045.5608 * Firefox v137.0.0 * Microsoft Defender v4.18.25020.1009-1.1.25020.1007 * Malwarebytes Premium v5.2.9.176-129.0.5196 * Macrium Reflect Free v8.0.7783 * CCleaner Free Portable 6.34.11482