cat > ./a.s <<eof
.section        .text._Z3foov,"axG",@progbits,_Z3foov,comdat
.hidden _Z3foov
.weak   _Z3foov
.type   _Z3foov,@function
_Z3foov:
  ret
eof
cc -c a.s

GRP_COMDAT deduplication is based on name, so after objcopy --localize-hidden,
the group may keep deduplication semantics. This may be undesired if the user
intention is to make the hidden symbols fully internal.

% objcopy --localize-hidden a.o b.o && readelf -Ws -x .group b.o

Symbol table '.symtab' contains 8 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 0000000000000000     0 FUNC    LOCAL  HIDDEN     5 _Z3foov
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    1 
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT    2 
     4: 0000000000000000     0 SECTION LOCAL  DEFAULT    3 
     5: 0000000000000000     0 SECTION LOCAL  DEFAULT    4 
     6: 0000000000000000     0 SECTION LOCAL  DEFAULT    5 
     7: 0000000000000000     0 SECTION LOCAL  DEFAULT    6 

Hex dump of section '.group':
  0x00000000 01000000 05000000                   ........


-G is similar.

See https://groups.google.com/g/generic-abi/c/2X6mR-s2zoc "GRP_COMDAT group with STB_LOCAL signature" for a generic-abi discussion.