The attached is a sample of a scrollable More/All tab. Import it to
tiddlywiki.com. I just think it it's a better experience than having the entire sidebar scroll.
I think an issue might be what height do you set the scrollble part to? Could it be calculated from the existing sidebar-segments?
<$scrollable class="tc-scrollable-demo">
<$list filter={{$:/core/Filters/AllTiddlers!!filter}} template="$:/core/ui/ListItemTemplate"/>
</$scrollable>