How to get deployment failed log in canonical maas

How to get the deployment failed log in canonical maas?
logs are not present in /var/snap/maas/current/log/

what version of MAAS, and what install method (snap/deb) ?

MAAS 3.5 installed by snap

first, take note of this:

Component Snap Command Debian Command
Regiond journalctl -u snap.maas.pebble -t maas-regiond journalctl -u maas-regiond
Rackd journalctl -u snap.maas.pebble -t maas-rackd journalctl -u maas-rackd
API Server journalctl -u snap.maas.pebble -t maas-apiserver journalctl -u maas-apiserver
Proxy (squid) journalctl -u snap.maas.pebble -t maas-proxy journalctl -u maas-proxy
NTP (chrony) journalctl -u snap.maas.pebble -t chronyd journalctl -u chrony

Log File Locations (Before MAAS 3.5)

Component Snap Location Debian Location
Regiond /var/snap/maas/common/log/regiond.log /var/log/maas/regiond.log
Rackd /var/snap/maas/common/log/rackd.log /var/log/maas/rackd.log
maas.log /var/snap/maas/common/log/maas.log /var/log/maas/maas.log

beyond this, did you look at the logs in the UI?