These I think are the relevant lines:
[ 3.510618] SELinux: Context system_u:object_r:qubes_qubesdb_daemon_exec_t:s0 is not valid (left unmapped).
[ 3.510715] (b-daemon)[311]: qubes-db.service: Unable to locate executable '/usr/bin/qubesdb-daemon': Permission denied
[ 3.510758] (b-daemon)[311]: qubes-db.service: Failed at step EXEC spawning /usr/bin/qubesdb-daemon: Permission denied
[ 3.512248] audit: type=1400 audit(1763553368.612:4): avc: denied { execute } for pid=311 comm="(b-daemon)" name="qubesdb-daemon" dev="xvda3" ino=1053100 scontext=system_u:system_r:init_t:s0 tcontext=system_u:object_r:unlabeled_t:s0 tclass=file permissive=0 trawcon="system_u:object_r:qubes_qubesdb_daemon_exec_t:s0"
[ 3.513781] systemd[1]: qubes-db.service: Main process exited, code=exited, status=203/EXEC
[ 3.513977] systemd[1]: qubes-db.service: Failed with result 'exit-code'.
[ 3.514262] systemd[1]: Failed to start qubes-db.service - Qubes DB agent.
[.[0;1;31mFAILED.[0m] Failed to start .[0;1;39mqubes-db.service.[0m - Qubes DB agent.
Per the first line, seems like an SELinux problem. If you do a search in the forum you can find this thread:
DVM’s comment here looks like it might help you: