and 難 glyph origins. Did 难/難 used to be a bird?
I'm going to give a simple answer first - I'm sure better more complete answers will come to follow.
Outlier

FORM
難 nán (also nàn) is composed of 堇 jiān and 隹 “bird,” which hints at the original meaning “type of bird.” 堇 gives the sound.
COMPONENTS
堇
In 難 nán (also nàn), 堇 jiān is a sound component, though this is not obvious in modern Mandarin.
隹
In 難, 隹 “bird” is a meaning component, hinting at the original meaning “type of bird.”
MEANINGS
nán
1 (orig.) name of a type of bird
2 ○ difficult
3 → trouble; adversity
nàn
1 (orig.) name of a type of bird
2 ○ difficult
3 → disaster; catastrophe

There's also a variant character:  (⿰鳥, if it doesn't display with you) which quite explicitly shows it's avian connection.
Outlier's reference comes from p. 307 &amp; 308 of 季旭昇's《說文新證》- this is where we will see the connection between the variant  and 難:





Here the ○ icon in Outlier's definition is an indicator of a phonetic loan. So, basically it is just a:

character that is &quot;borrowed&quot; to write another homophonous or near-homophonous morpheme

and this is confirmed by《說文新證》's:

假借

explanation.

隹 replaces ---&gt; 鳥

堇 was seemingly always there giving the character its sound



&quot;⿰x&quot; being replaced by &quot;⿰又x&quot; is a separate question but it's not totally uncommon, think: 艱 → 艰.