My comprehension, so far:
The "Unicode" column under the Glyps/Edit-tab just shows those of "Characters". … which determines the keys to press when typing it into a text.
The "Unicode" should be the one to be assigned to the glyph when opening the .svg in FontForge, shouldn't it?
If that ↑ is true at all, how to assign the unicode for a ligature-glyph?

Hi there sorry i'm a novice and only just starting looking into this myself this morning but have been using a great intro guide video on youtube (link below). From that i think you just add a new glyph and type both letters in the char box.

https://youtu.be/skv1Dj7232w?t=677

@ RuaridhW:

Thanks for your engagement!

But typing the "letters" into the char box specifies what keys to press to type the ligature not the unicode for the new ligature-glyph.
Meanwhile I found that setting the name to "uni#####" (not U+#####)¹ will assign the unicode.
¹) FontForge declines the use of "+"-signs in character names

Currently struggling with FontForge to get characters with unicodes beyond "Basic Latin" from FontForge's .sdf to the usable .ttf / .otf Font.

btw: the best (but also partly incomplete and not always precisely correct) video I found is:
https://vladar.bearblog.dev/creating-fonts-with-inkscape-and-fontforge/

awesome many thanks for both the tip and link!