Global Nav has been a gigantic weakspot in SharePoint forever. I suspect the use of SPFX Extensions (I think they are called) are supposed to close this gap, but it will be considered Custom Development.
I would love to see Microsoft actually pull off some kind of Out-of-the-Box mega menu that can be turned on, turned off, and customized by administrators not by code, and made available on EVERY site collection, regardless of Group Site, Modern Team Site, or Communication Site.
For years, I've used a custom HTML/CSS/JS Mega Menu embedded in all site collections using UserCustomActions, and it has been a critical component of adoption. With modern sharepoint and lack of what I'll call "easy" customization options, we are starting to lose out on those benefits, and having to tell users "click here to go to the home page, then click where you really want to go from there", which is do-able, just inconvenient.