Reading the cardinality with the ternary operator ($element['#cardinality'] ?: NULL) without testing beforehand if the array key exists triggers a warning shown as error by Drupal:
Warning: Undefined array key "#cardinality" in Drupal\choices_autocomplete\Element\ChoicesAutocomplete::processChoicesAutocomplete() (line 58 of modules/contrib/choices_autocomplete/src/Element/ChoicesAutocomplete.php).
Either use the NULL coalescing operator (which looks quite strange when passing NULL: $element['#cardinality'] ?? NULL) or explicitly check with isset().
This patch works for me! Installed it on my Drupal 10.2.2 site running PHP 8.2 and the error went away when I applied the patch.