I tested with the upgrades. The ticket is done and I verify that it works as expected. See notes below:

Consider this scenario: I install fresh PXC Operator 1.15.0. It has auto resize enabled by default (and no possibility to disable, as we know very well). I try it - resize pxc storage from 6G (the default) to 10G. Works OK. Then I upgrade directly to 1.16.0 (main branch). I perform the upgrade using the default cr.yaml, which has storage == 6G (the default)
Result: Storage remains 10G (as it was resized in 1.15.0)
Question: As we know, in 1.16.0 it was decided that resize will be disabled by default. But we also expect when we upgrade to retain the previous behavior. So, why am I not seeing the auto upgrade (retained from 1.15.0) to trigger the downscaling from 10G to 6G?

Answer (after discussing with the team): in this case we don't retain the previous behavior: in v1.15.0 there's no way to enable/disable PVC resize and in v1.16.0 it's disabled by default, also downscaling is not possible (The user cannot shrink the size of an existing PVC object.) but upscaling wouldn’t work either, because the behavior won't change if you upscale or try to downscale, it's disabled by default.

Hi,

JFH: enableVolumeExpansion was also added to hotfix releases 1.14.1 and 1.15.1 released in October. We need to additionally recheck 1.15.0 & 1.15.1 update to 1.16.0.

After discussing with the team, it was acknowledged that we don’t have a strict convention to follow with regard to whether the commented out example values in the cr.yaml file will be the default ones or not. So, it could be either # enableVolumeExpansion: true or # enableVolumeExpansion: false it doesn’t matter.

Please, change the commented out example option in cr.yaml
from

to

The new option was added spec.enableVolumeExpansion, and we have disabled PVC resize by default.