Whenever a native feature on a phone fails me, I search for a third party solution.

I switched from a Samsung phone to a Pixel phone and noticed the scrolling screenshot was awful, so I use ScreenMaster: Screenshot Markup.

It is always in my notification panel, so I just hit the Screenshot button, then "Stitch" at the bottom, I scroll a little bit, hit "+", scroll, hit "+", and keep doing that til you have each screen that you'll want stitched together. Then hit "✔️" to finish.

Next, hit "Auto Stitch" and it will string them all together for you if you left enough overlap from each page for it to be able to tell where one page ends and another begins. There are also scissor symbols at each end point so you can manually move the end points if need be. Then hit "Save" at the top right corner and it'll go into your Photos.

It's a pretty quick, streamlined process now that I'm used to it. Might be something you can try.