Fix Verticals

I wonder if there's an FCPX tool to fix vertical lines for example for architecture shots? Many thanks for any hint!

Fix what about verticle lines? You do have rotation parameters to level a shot out. But I've no clue what "fix verticle lines" means. What lines, fix what exactly?

I was thinking of some sort of keystone correction for converging lines.

Of course, I can do it manually by changing the distortion but I wonder if there are some more comfortable tools like they are in image editing software:

The issue is the camera lens warping the image around the edges. There are fisheye lens correction plugins that help with this, but they're usually made specifically for certain cameras such as the Hero or DJI drone cameras. There may be some generic ones. FCPX comes with one in the Distortion category of the Effects browser. I also have two categories called Lens Filters and Utility, no clue who I got that stuff from, but some useful tools in there. Maybe someone knows of a plugin I'm not aware of.

I don't know a plug in to make a "kind of one click fix"
But why not use the "Distort" in the Video Inspector?

Lens correction is a futhermore issue. I simply use the built-in fisheye effect to address this but I'd interested in a better tool.

To encounter the keystone issue, I use Distort in the Inspector, of course. But it's a lot of work to fix the lines manually. It would be great to have a tool that allows you to mark all the converting links, press enter and volia, they are all perfectly vertical. To sum it up, something like the "Perspective Warp" tool in Photoshop.

Alex 4D has a free tool you might be able to use:
alex4d.com/final_cut_plugins/alex4d-free...ide-angle-fix-effect

Sight-Creations (me...) has a different approach - an easier distortion tool than the standard FCPX distortion and a Fisheye Reduction effect that can be used in conjunction with the Lens Distortion Fix effect:
(demo/tutorial video) — you can decide if you want to take it further. These are not "one-click" fixes (video is constantly changing).

I'm not aware of any others...

Fantastic! This might help indeed, I'll give it a try! Many thanks!