Lets see (this is from Alma, but should be close enough):
# dnf module list postg*
Last metadata expiration check: 0:19:24 ago on Wed 03 Nov 2021 09:35:31 AM EET.
AlmaLinux 8 - x86_64 - AppStream - SBL
Name Stream Profiles Summary
postgresql 9.6 client, server [d] PostgreSQL server and client module
postgresql 10 [d] client, server [d] PostgreSQL server and client module
postgresql 12 client, server [d] PostgreSQL server and client module
postgresql 13 client, server [d] PostgreSQL server and client module
Hint: [d]efault, [e]nabled, [x]disabled, [i]nstalled
# dnf list postg*
Last metadata expiration check: 0:21:41 ago on Wed 03 Nov 2021 09:35:31 AM EET.
Available Packages
postgresql.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-contrib.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-docs.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-jdbc.noarch 42.2.3-3.el8_2 appstream
postgresql-jdbc-javadoc.noarch 42.2.3-3.el8_2 appstream
postgresql-odbc.x86_64 10.03.0000-2.el8 appstream
postgresql-odbc-tests.x86_64 10.03.0000-2.el8 appstream
postgresql-plperl.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-plpython3.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-pltcl.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-server.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-server-devel.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-static.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-test.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-test-rpm-macros.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-upgrade.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
postgresql-upgrade-devel.x86_64 10.17-1.module_el8.4.0+2480+895597ab appstream
There we saw package ‘postgresql’. Lets switch to stream 13:
# dnf module enable postgresql:13
Last metadata expiration check: 0:22:12 ago on Wed 03 Nov 2021 09:35:31 AM EET.
Dependencies resolved.
===================================================================================================================
Package Architecture Version Repository Size
===================================================================================================================
Enabling module streams:
postgresql 13
Transaction Summary
===================================================================================================================
Is this ok [y/N]: y
Complete!
Red Hat instructions show additional commands: Chapter 6. Managing versions of Application Stream content Red Hat Enterprise Linux 8 | Red Hat Customer Portal
What did we get?
# dnf module list postg*
Last metadata expiration check: 0:22:28 ago on Wed 03 Nov 2021 09:35:31 AM EET.
AlmaLinux 8 - x86_64 - AppStream - SBL
Name Stream Profiles Summary
postgresql 9.6 client, server [d] PostgreSQL server and client module
postgresql 10 [d] client, server [d] PostgreSQL server and client module
postgresql 12 client, server [d] PostgreSQL server and client module
postgresql 13 [e] client, server [d] PostgreSQL server and client module
Hint: [d]efault, [e]nabled, [x]disabled, [i]nstalled
# dnf list postg*
Last metadata expiration check: 0:22:34 ago on Wed 03 Nov 2021 09:35:31 AM EET.
Available Packages
postgres-decoderbufs.x86_64 0.10.0-2.module_el8.4.0+2484+85259292 appstream
postgresql.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-contrib.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-docs.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-jdbc.noarch 42.2.3-3.el8_2 appstream
postgresql-jdbc-javadoc.noarch 42.2.3-3.el8_2 appstream
postgresql-odbc.x86_64 10.03.0000-2.el8 appstream
postgresql-odbc-tests.x86_64 10.03.0000-2.el8 appstream
postgresql-plperl.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-plpython3.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-pltcl.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-server.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-server-devel.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-static.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-test.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-test-rpm-macros.noarch 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-upgrade.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
postgresql-upgrade-devel.x86_64 13.3-1.module_el8.4.0+2484+85259292 appstream
We still see package ‘postgresql’ but now its version is not 10 any more.
The names of packages are same in every stream.
These streams have two profiles: ‘client’ and ‘server’. The latter is default. Profiles are lists of packages, like yum groups.
# dnf module info --profile postgresql:13
Last metadata expiration check: 0:35:43 ago on Wed 03 Nov 2021 09:35:31 AM EET.
Name : postgresql:13:8040020210411111349:9f9e2e7e:x86_64
client : postgresql
server : postgresql-server
Name : postgresql:13:8040020210610141046:522a0ee4:x86_64
client : postgresql
server : postgresql-server
Therefore,
dnf module install postgresql
// is same as
dnf install @postgresql
// and in practice same as
dnf install postgresql-server