It's like with migrating from Windows to Linux. When Windows XP came out of support I moved my mum and dad who were in their early 60's from XP onto Xubuntu. They already used Chrome and LibreOffice so it's an easy move. The hard part wasn't adjusting to a new desktop, but the install process.
Moving off WP is the same. Find a solid, reliable modern PHP CMS with a decent core, get it set up for the client and they'll likely be fine. They'll likely benefit from a cleaner, more intuitive admin that isn't full of banners nagging them to buy a paid version of a plugin they don't need.
Plus maintaining WP on behalf of clients' probably isn't worth your time, particularly if it's vanilla WP rather than Bedrock, unless it's a favour for a friend or family. If you're a professional I suspect it's just not worth going after that business.