With such downvotes, I start to think electron hate is a cult.
The Web still sucks, and we don't need to shove The Web into native applications. Learn to make an actual program. Heck, QT exists, learn to use it.
I'm not saying you can't use an HTML layout engine for help and info screens, but for the entire program it's pants-on-head stupid. The time spent trying to warp one's web designer skills to make an "app" could have been used to learn how to make an actual application that would've been portable, and take less than a gig of RAM.
I use Teams at work, and it's taking 300+ MB of RAM on startup when it's basically a glorified chat client. Insanity.
90% of the time I'd agree with this sentiment, but modern email clients need to be able to render rich web content. A browser engine integration is just the reality, at some level.
No they don't.
I get more HTML emails than plain-text. I won't switch to a mail client that can't render the majority of my inbox.
Its not clear to me you need anything resembling a modern web browser to render HTML emails. Do they even commonly use HTML5 features?