<button is="my-button">
<my-button></my-button>
Aside from this, safari has great support for WCs and is just as capable as any other evergreen browser.
https://developer.mozilla.org/en-US/docs/Web/Web_Components/...
If you're correct about Safari's level of support can you referf me to where it supports connectedCallback?
It's been supported for years AFAIK. As long as you extend HTMLElement, and not some other element, everything will work as expected
Aside from this, safari has great support for WCs and is just as capable as any other evergreen browser.