gcc 11 compatibility?

[Mike Liao <mikeljx 126 com>]

I've recently updated my gcc to version 11, and I can't compile my 
project under thec++20 standard.

Here is part of the errors gcc reports:

/usr/include/glibmm-2.68/glibmm/variant.h:910:24: error: expected 
unqualified-id before ‘)’ token
  910 |   Variant<VariantBase>();
      |                        ^
/usr/include/glibmm-2.68/glibmm/variant.h:971:25: error: expected 
unqualified-id before ‘)’ token
  971 |   Variant< Variant<T> >();
      |                         ^
/usr/include/glibmm-2.68/glibmm/variant.h:1024:26: error: expected 
unqualified-id before ‘)’ token
 1024 |   Variant<Glib::ustring>();
      |                          ^
/usr/include/glibmm-2.68/glibmm/variant.h:1190:24: error: expected 
unqualified-id before ‘)’ token
 1190 |   Variant<std::string>();
      |                        ^
/usr/include/glibmm-2.68/glibmm/variant.h:1232:30: error: expected 
unqualified-id before ‘)’ token
 1232 |   Variant< std::pair<K, V> >()
      |                              ^
/usr/include/glibmm-2.68/glibmm/variant.h:1281:29: error: expected 
unqualified-id before ‘)’ token
 1281 |   Variant< std::vector<T> >()
      |                             ^
/usr/include/glibmm-2.68/glibmm/variant.h:1350:41: error: expected 
unqualified-id before ‘)’ token
 1350 |   Variant< std::vector<Glib::ustring> >();
      |                                         ^
/usr/include/glibmm-2.68/glibmm/variant.h:1476:39: error: expected 
unqualified-id before ‘)’ token
 1476 |   Variant< std::vector<std::string> >();
      |                                       ^
/usr/include/glibmm-2.68/glibmm/variant.h:1552:29: error: expected 
unqualified-id before ‘)’ token
 1552 |   Variant< std::map<K, V> >()
      |                             ^
/usr/include/glibmm-2.68/glibmm/variant.h:1625:33: error: expected 
unqualified-id before ‘)’ token
 1625 |   Variant<std::tuple<Types...>>()
      |                                 ^

Does this have anything to do with some new rules introduced in c++20?