Looking in your 21MB file is see alot of the old mix nodes which have to be replaced with the new color mix node (and one float mix…) for the trousers… and also there are mutliple Mix Shader node to mix some values… which should be a flaot mix too… for the shirt
…and for the hankerchief, hair, etc… → mix float
I guess because the Ellie character Rig was for 3.0 and you are using 3.5…
The mixRGB node was changed in 3.4…
See also here:
or: