No you are not doing anything wrong, Audacity has decided to always import 24-bit files at 32-bit resolution instead of 24-bit - even if default sample format (Quality Preferences) is 16-bit or 24-bit. See https://forum.audacityteam.org/t/change-dither-to-none-in-quality-settings/30777/11 . This contrasts to seemingly more expected behaviour for FLAC https://forum.audacityteam.org/t/change-dither-to-none-in-quality-settings/30777/14 .
I know of no necessary reason to always import 24-bit files as 32-bit, so you can request it be changed and we’ll count your vote towards it…
I’ll see your vote is counted - the votes are kept at http://wiki.audacityteam.org/wiki/Feature_Requests but you need to request a Wiki account to edit the Wiki.
If you want to vote for other features on that Feature Requests list, please write to our feedback address .