Hi John and welcome to the forum:
First I agree with my colleagues that you may require an upgrade to get better performance at higher ISO, and I would recommend mirrorless as, having had the 80D and 90D, the 90D is no great improvement, in fact arguably the opposite as it crammed more pixels into the same space.
As Ricky and Ernie have both suggested, I would recommend one of the new R-series bodies, and definitely go full-frame, the sensor being bigger they should have better noise performance than a crop body. The question as to what model is tied to your budget.
If you can afford it, I would suggest going for either the R6 or R6MkII, both are brilliant cameras, use the same battery as your 80D, have face and eye tracking that is superior to lower models and a better build. They have In-Body Image Stabilization (IBIS) that helps to reduce camera shake in dim light and lower shutter speeds.
You can use your current EF lenses with those bodies via the Canon EF-RF adapter, and so far I have never had an issue with them. If you currently use EF-S lenses, although they will physically connect to a FF body, I would not recommend them as their narrower cone of projection onto the sensor will not cover a FF sensor and you will end up cropped by a factor of 2.56. If you are going to sell your 80D, sell the lenses with it to help fund your purchase.
You can pick up a refurbished camera from Canon (like new, with limited warranty) as follows:
R6: https://www.usa.canon.com/shop/p/refurbished-eos-r6-body
R6MkII: https://www.usa.canon.com/shop/p/refurbished-eos-r6-mark-ii-body
If you can afford to invest in glass, then look at the range of RF glass they are brilliant optics.
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
