Add vertical "before and after" slider to DEVELOP image adjustments

Would the Reference and Active view in Develop give you what youre looking forTo enable Reverence view, click the “R|A” icon below the image preview area in the Develop module or, use the shortcut Shift + R. Then, either drag a reference photo from the filmstrip to the Reference view to compare with the active photo or, right-click (Control -click on Mac)  on any image in the filmstrip and choose “Set as Reference Photo” from the context sensitive menu.

you can edit the active image in real time

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LR has Before/After Left/Right Top/Bottom Split views, e.g.

I think you're asking for the divider to be adjustable left/right or top/bottom, as in this request?

https://community.adobe.com/t5/lightroom-classic-ideas/p-split-screen-divider-with-movement-capabilities-for-comparing-before-and-after/idi-p/13445538