Don''t "overthink it".
Rice and wheat flour glues are very simple mixtures of flour and water, the dissolved starches become sugars and form the bond when dried. Mucilage is based on a similar principle but uses fruit sugars/resins. Commercial mucilage probably has stabilizers added.
Oldest form is "gum tragacanth":
https://en.wikipedia.org/wiki/Tragacanth, but I suspect it'd be quite a bit more costly and demanding of effort to make yourself.
Unless you're just one of those guys who likes to try out traditional recipes like me. I once tried to make marzipan from scratch using almonds harvested from abandoned and seeded stock remnants from an old commercial field bordering a bike path I use.
First step was to roast them. 20 minutes into the process, "BANG ! POP!" from the oven (before microwaves were common).
When I checked, most of them had become slightly burnt and a few had popped like popcorn with "interesting" results.
(even though I was using very low temperature).
Fortunately it cleaned up easily, and after they'd cooled I decided to sample one. UGH. Very bitter. Forget the marzipan.
I found out only recently there are 2 types of almonds, "sweet" and "bitter". Bitter actually has a higher percentage of cyanide and it's actually possible to poison yourself with an overdose.
Good thing I didn't wind up making marzipan after all.
The moral here is don't eat any strange labels with unknown substances on them.
