SQL Server 2019

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CREATE TABLE tbl_2 (
    qtype int primary key,
    qname nvarchar(MAX)
)
CREATE TABLE tbl_1 (
    id int, 
    disabled bit,
    qtype int,
    qtype_enabled as (case when disabled = 1 then qtype end) persisted,
    foreign key (qtype_enabled) references tbl_2 (qtype)
)
insert into tbl_2 values (1, 'abc')
1 rows affected

-- should work because the primary key is there
insert into tbl_1 values (1, 1, 1)
1 rows affected

-- should work because the row is disabled
insert into tbl_1 values (2, 0, 1)
1 rows affected

-- should fail because the row is enabled and the primary key is not there
insert into tbl_1 values (3, 1, 3)
Msg 547 Level 16 State 0 Line 2
The INSERT statement conflicted with the FOREIGN KEY constraint "FK__tbl_1__qtype_ena__25869641". The conflict occurred in database "fiddle_040d777ea10340bcbb057a2ec3c28385", table "dbo.tbl_2", column 'qtype'.
Msg 3621 Level 0 State 0 Line 2
The statement has been terminated.