APEX 24.1.7, 24.2.1
CREATE SEQUENCE test_checkbox_seq MINVALUE 1 noMAXVALUE INCREMENT BY 1 START WITH 1 NOORDER NOCYCLE;
create table test_checkbox (
id number not null
,test_tf number(1) default 0 not null
,text varchar2(10)
);
insert into test_checkbox (id, test_tf, text) values(test_checkbox_seq.nextval, 0, 'xx 1');
insert into test_checkbox (id, test_tf, text) values(test_checkbox_seq.nextval, 0, 'xx 2');
insert into test_checkbox (id, test_tf, text) values(test_checkbox_seq.nextval, 0, 'xx 3');
In APEX, the IG region is defined as
select id
,test_tf
,text
from test_checkbox
column test_tf column is defined as Checkbox, checked: 1, unchecked: 0, Default: Static: 0
open the page
double-click on one line's text field
click on another line
The result:

If now one tries to save the page, then…

Of course. Or not of course?
Well, if the checkbox column is set in UI as not mandatory, everything is OK, no error messages and data in the DB is, as supposed:
