There is no option to Create a new entity if it is missing

I don't understand clearly. It automatically creates an entity if it does not exist, but in the widget there is an option to lock the creation of a new entity. Maybe you should try before you ask

after updating to version 2.0.2, such an option was actually found in the field widget. Thank you.

I'm sorry, this still doesn't work for me. When I add a custom entity with bundle as the first column and edit it, no errors occur. When editing again, only the entity with id=1 is shown in all rows of this column. This can be seen in the attached screenshot of the editing form.

do you clear the cache? I'm not testing with a custom entity but it still works for content and node taxonomy

Of course I cleared the cache.
I am using an entity generated by content entity builder.

Now it becomes clear that when you initially edit rows, the column is correctly written to the database, but when you reopen the editing form, incorrect, repeated values ​​are entered into the field widgets.

The same happen with the taxonomy column, but the pattern of what is happening is not clear.

does it work without generated? I remind you that the data field is not an entity field, if your generator is based on schema storage this will not work. because entity will store entity id in database but it will be generated with field settings