These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.19 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/libaio-0.3.113_p8::gentoo  USE="-static-libs -test" 74 KiB
[ebuild  N     ] acct-group/mysql-0-r3::gentoo  0 KiB
[ebuild  N     ] sys-libs/liburing-2.15:0/2::gentoo  USE="-examples -static-libs -test" 538 KiB
[ebuild  N     ] app-arch/lz4-1.10.0-r1:0/1.10.0-meson::gentoo  USE="-static-libs -test" 379 KiB
[ebuild  N     ] acct-user/mysql-0-r3::gentoo  0 KiB
[ebuild  N     ] dev-db/mariadb-connector-c-3.4.9-r2:0/3::gentoo  USE="curl -gnutls -kerberos -static-libs -test" 1352 KiB
[ebuild  N     ] dev-db/mysql-connector-c-8.0.41-r1:0/21::gentoo  USE="-ldap -static-libs" 477295 KiB
[ebuild  N     ] dev-db/mysql-init-scripts-2.3-r8::gentoo  0 KiB
[ebuild  N     ] dev-perl/DBD-MariaDB-1.240.0::gentoo  USE="mariadb -minimal -mysql -test" PERL_FEATURES="ithreads (-debug) -quadmath" 185 KiB
[ebuild  N     ] dev-db/mariadb-10.11.19:10.11/18::gentoo  USE="backup pam perl server -bindist -columnstore -cracklib -debug -extraengine -galera -innodb-lz4 -innodb-lzo -innodb-snappy -jdbc -jemalloc -kerberos -latin1 -mroonga -numa -odbc -oqgraph -profiling -rocksdb -s3 (-selinux) -sphinx -sst-mariabackup -sst-rsync -static (-systemd) -systemtap -tcmalloc -test -xml -yassl" 112129 KiB
[blocks B      ] <dev-db/mariadb-11.4.7-r0 ("<dev-db/mariadb-11.4.7-r0" is soft blocking dev-db/mariadb-connector-c-3.4.9-r2)

Total: 10 packages (10 new), Size of downloads: 591948 KiB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (dev-db/mariadb-10.11.19:10.11/18::gentoo, ebuild scheduled for merge) pulled in by
    =dev-db/mariadb-10.11.19

  (dev-db/mariadb-connector-c-3.4.9-r2:0/3::gentoo, ebuild scheduled for merge) pulled in by
    dev-db/mariadb-connector-c:= required by (dev-perl/DBD-MariaDB-1.240.0:0/0::gentoo, ebuild scheduled for merge) USE="mariadb -minimal -mysql -test" PERL_FEATURES="ithreads (-debug) -quadmath"


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages