As hinted by Mathias below I can confirm that the component does not work anymore with Vaadin 23.2. Unfortunately, the new multi-select-combobox included with Vaadin 23.2 does not provide the select-all features so it cannot be used to replace this one...
I've opened a bug on GitHub : https://github.com/vaadin-component-factory/multi-combo-box-flow/issues/23