I'm not sure what the best way to quantify this is but this is what I have come up with.

If the % of all users here https://caniuse.com/avif is greater than or equal to WebP's % of all users here https://caniuse.com/webp at any time before 2026, then this will resolve to YES, otherwise it resolves to NO.

To be extra clear, it is the % number on the right hand side of the equal sign on the above pages I linked, in the upper right corner of the page.

For example, currently avif is at 85.41% and WebP is at 96.68%, if avif gets to 96.68% (and WebP doesn't change in that same time period) then this will resolve to YES.