This has been fixed in GParted 1.3.0 released 2021-May-03 [1], by the merge of [2].
Thanks, Mike Fleetwood (GParted Developer) [1] https://gparted.org/news.php?item=238 [2] Support resizing open LUKS2 encryption mappings by supplying the needed passphrase https://gitlab.gnome.org/GNOME/gparted/-/merge_requests/80
