Disagreement between glib and gcc after gcc downgrade

I updated my distro a week ago Linux *** 5.10.41-1-MANJARO x86_64 GNU/Linux recent *gcc and gcc-lib* version 11.1.0 But need to work with gcc 10.2.0 and its coworker gcc-libs 10.2.0 I downgraded gcc and glib according to this guide There is no problem with this but other thing get break like *Firefox, Chromium etc* and it gives the following error

firefox
/usr/lib/firefox/firefox: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /usr/lib/firefox/firefox)

How can I downgrade *gcc* and coworker libs which I think its *glib* I don't know how to deal with *glib*

sudo downgrade glib-
glib-compile-resources  glib-genmarshal         glib-mkenums
glib-compile-schemas    glib-gettextize

Should I downgrade a *glib* thing belongs to them?