I'm not sure what is holding you to upgrade to 90d, in my case it's better in every possible way, except two things:
1. Body is not all metal (though metal-plated), but looks sturdier than R6 IMO.
2. You cannot deep-program AF point buttons. For example, both on my 7D/mk2 and 5d4 I mapped back AF-ON to be One Shot and * button to be Servo with separate AF points (Spot AF and Zone). You cannot go that deep on 90d. That was a massive blow for me, but I learned to overcome it by using shutter button for AF (default) and AF-ON mapped as a Servo switch.
3. No dual card slots (with CRAW and high-capacity cards, I don't care for that at all)
But that's where drawbacks end for me. Speaking of its AF module, I find it improved over 7D2 and much improved over 7D. It's on par with my 5D4, slightly less precise with 50mm f1.8 STM, but then again that lens isn't the most precise one and it's sharper on FF overall as it's not pushing the optics beyond normal levels. LiveView on the other hand rivals mirroless cameras. Super fast, super smart, face recognition with eye-find focus and Focus Peaking for manual lenses.
All in all, I have effectively moved from 5d4 to 90d. With a price of 1k euros, it's a steal for such a great and modern aps-c camera.