dang, well, i aint gonna try haha. no sense in doing so.
Simple stitching.

Now work that out with all the complex curves.
Yup, i like extensions and the pro version. I feel bad for the web version(including shop) that cant use loftâŚ
im noticing that when i try to use solid tolls on the top circle surface to make a 11.75 radius hole all the way through, that it takes about 2 minutes for solid tools to complete the operation⌠its only passing through the circle face and square, not the loft⌠any idea why it is taking so long?
Solid tools, like most extensions, needs to work through all the geometry that is involved, it doesnât know you just want a hole in this bit. Sometimes it is better to just make a hole.
hmm, ok, so i need to think this through a we bit different. if i draw a hole on the top circle, and remove it, i need to skin it all the way down to make the actual âcylenderâ shape rather than just an open part.
this is the end goal

Draw a circle and push pull it to the bottom and you have your cylinder.
im an idiot⌠push pull tool⌠i blame tv for this hahaha
yeah, i just realized it as you were typing⌠i cant believe i forgot the most BASIC tool in sketchup hahaha
Youâre not the first person to over complicate something.
i get so used to a tool like curvi loft, solidworks, fusion, and then it gets all mixed up⌠Im trying to stick with just SU pro. f360 and solidworks are great but doesnt work like my brain does. SU pro works like my brain
finished

you are running 2021 and I am on 2020 so I cannot open your example on my version of sketchup so I replicated it, then simply captured the whole thing and launched curviloft âalong (single) pathâ and it came out fine. Can you check hidden geometry to se if anything else is there that might confuse curviloft ?
There is a bit of a dark art to understanding how some of fredos extensions work. As an example here are four identical âreplicationsâ of the shape. I created one then made 3 copies, so there is no extra or hidden geometry. What I have done is manipulate the edges in various ways.
As you can see only one combination gives the desired result.

how did you manipulate the edges in various ways? I am curious?
thansk
As I said, itâs a Dark Art and unless you are a member of slitherin I canât tell you. (so sad that I know that at my age)
Having said that, I flipped one, rotated another and used revert curves on a third. And most importantly if I do it again I cannot consistently reproduce the results.
So knowing what I did doesnât actually help.
Well, â â â â , im from one of the other houses⌠hahaha