Using the keystone correction function, it is important to set the anchor points precisely. Sometimes they are difficult to recognize, or the image structure is very complex. It would help a lot if a magnifying glass appeared and enlarged the image section as soon as you move an anchor point.
Requested here a while ago: https://support.captureone.com/hc/en-us/community/posts/9740851622557-Keystone-tool-Loupe-showing-position-of-adjustment-points
... and for the straighten tool too.
https://support.captureone.com/hc/en-us/community/posts/15181162902685-Offer-the-option-to-automatically-activate-a-loupe-when-positioning-straighten-and-keystone-tools