@mitu From what directory do i do the
apt install libsdl2-net-2.0-0?

It doesn't matter.

and then from what directory do i do the standalone
installation and extraction from https://buildbot.scummvm.org/dailybuild ... 6e6.tar.xz ?

and in which order?

Not sure what you mean here, your post indicated that you've already done this and you get an error when you're executing the new scummvm. Just extract the archive obtained from the ScummVM Buildbot using site with tar, i.e.

tar xJf /path/to/<archive_file>

and you'll be getting a new folder containing the ScummVM installation. You can then rename/move the folder as you like.

@mth75 The patches added by the RetroPie install script work only with the branch/version specified in the script. If you'd like to get the latest dev version, you should also remove the .diff being applied.