To reproduce the issue:
Create an Illustrator file
Create a new text frame, type anything and set font to Stratos (OTF) (as available from Adobe Fonts)
Export PDF through "Export for screens"
Trying to copy paste text fails

The issue occurs more precisely with characters that have glyphnames like uniXXXX.
Almost all characters in Stratos have uniXXXX names, even though they are present in the
AGL. So "A" has "uni0041" as glyphname.
We were under the assumption that uniXXXX glyph names were accepted.
The issue only seems to occur with .otf fonts.

See the two attached PDF's for
251119-Stratos-ttf.pdf will correctly copy all the characters
251119-Stratos-otf.pdf will copy the characters as " " ( <0x2000> )

The specifications for AGL say:
Font producers are strongly encouraged to respect this specification when naming the glyphs for their fonts.
Generally, multiple names can be mapped to the same string. For example, the components ‘Lcommaaccent’, ‘uni013B’, and ‘u013B’ all map to the string U+013B.
So they recommend using 'A' as glyph name, but 'uni0041' should also be accepted.