Interactive Delete: There’s a tool button for it in the bottom of the right hand toolbar, both in eeschema and pcbnew. (You implied there’s no button.) You can assign a hotkey for it in Preferences.
BTW, one change after v5 is that there are much more functions which can have a hotkey or shortcut. Just search in the list. I haven’t compared but the list may have been doubled or tripled. (EDIT: I tested with Help->List Hotkeys dialog. In v5 it takes 10 Page Down presses to scroll down the list of pcbnew hotkeys. In v5.99 it takes 30.)
In Board setup section: “eeschame”. For some reason that’s a common mispelling, I do that sometimes, too. What a schame. 
One thing worth mentioning about text replacement variables in footprints could be that all symbol and sheet variables are available in footprints, as well. You can for example add a new field MPN to a symbol in the schematic. Then update the pcb. Modify the footprint in the board, adding a text field:
And you will have the manufacturer part number visible in the Fab layer.
It’s great that you’ve got even instructions for reporting bugs. A smallish detail: videos can be uploaded and attached directly to the report. That’s the recommended practice because external links tend to deteriorate and may have other problems. All reports should be as self-contained as possible, although links to background information is OK.
The most important component “under the hood” change in KiCad 6 is the schematics and layouts’ file format. My understanding is that work there is complete. This means that any work you do has good chances that will be readable by the official KiCad 6.0.
Work there isn’t quite complete, although the final v6 should be able to read the files created and edited now. We are still waiting for curved polygons which requires a file format change in the pcb file format. When that’s introduced and you use curved polys the file won’t be readable by older nightly builds. Bugfixes are also theoretically possible. One unplanned change to file format lately was a fix which also introduced a new feature; you can see the history here.
With curved polygons there should come also a (significant?) UI change, namely “constraint manager”. It’s basically continued work from before v5.1 which was introduced in the fund raising campaign back then and in its old form can be seen shortly in the donation campaign youtube video (“improved drawing tools”). I hope they get it ready this time. In the merge request Seth mentions “work package” which possibly means it’s outsourced as a paid job.
Curved polygons and its editing system should make creating and editing complex board outlines much easier. In v5.1 you have to use separate straight lines and arcs. Drawing them is something from easy to difficult, and editing is always painful because you have to move and edit several lines if one is changed. And making and keeping it continuous was sometimes impossible. So, when these features are merged in, pay attention to them.
In my testing, I found that the fillet function only works with 90-degree angles.
In my testing 45-degree angles work, too.
Fillet editing (for existing fillets) was enhanced recently, see Post-v5 new features and development news for explanation and a video. It’s a big enhancement, although doesn’t do push&shove.
