Unattended-upgrades keeps versioned kernel packages because they don't match known kernel package patterns:
...
Keeping auto-removable linux-modules-4.18.0-14-generic package(s) because it would also remove the following packages which should be kept in this step: linux-image-unsigned-4.18.0-14-generic
...
For reproduction see LP: #1795696, but running u-u with --verbose.
Unattended-upgrades keeps versioned kernel packages because they don't match known kernel package patterns:
... 4.18.0- 14-generic package(s) because it would also remove the following packages which should be kept in this step: linux-image- unsigned- 4.18.0- 14-generic
Keeping auto-removable linux-modules-
...
For reproduction see LP: #1795696, but running u-u with --verbose.