SQL Server 2022

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DECLARE @STring VARCHAR(MAX) = 'Qfntoqgjqnvwhtoupqjc
T-M123-1234567890
Jfjxnankcnvnnsmnv
Fjndncnrjdnnc
T-M123-1234567891
Ddndjjjjdmxndbx
Dnnxnxn
T-M123-1234567892
Dhdhdjdjxnn
T-M123-1234567893
Hdjxndnd
Dbxbxn
T-MDnxnxnnx
Ndndndn
Dnxdn
T-M123-1234567894
Dhdhd
T-M123-1234567895
Djdndj
T-MDjdndj
Dndn
T-M123-1234567896
Sndndjd
T-M123-1234567897
Jerrf
Gjfjfdjdnd
T-M123-1234567898
Rjrjrjf
Fjdndjf
T-M123-1234567899
Jdjffj
T-M123-1234567900
Ffnm
T-M123-1234567901
Rmdnd
Dxndnxn
T-M123-1234567902
Djdjrjj
Dndnd
T-M123-1234567903
Djdjdjd
Dndndndn
T-M123-1234567904
Dnxndn
T-M123-1234567905
Dndndnd
T-M123-1234567906
Snnddn
T-M123-1234567907
Nedndn
T-MNsnddn
Sndsn
T-M123-1234567908
Nenene
Nenddn
T-MDddnns
Nenenene
Ejej
T-M123-1234567909
Jeejjeje
Jeejje
T-M123-1234567910
Wirhdndn
Endndn
T-M123-1234567911
Jedj
Ssn
Qycm
Ddn'

SELECT *
FROM (
    SELECT S.*, ROW_NUMBER() OVER(ORDER BY S.ordinal) AS RowNum
    FROM STRING_SPLIT(REPLACE(@String, CHAR(13), ''), CHAR(10), 1) S
    WHERE S.value LIKE 'T-M%'
) S
WHERE RowNum = 20

value	ordinal	RowNum
T-M123-1234567907	49	20

SELECT *
FROM (
    SELECT J.value, J.[key], ROW_NUMBER() OVER(ORDER BY CAST(J.[key] AS INT)) AS RowNum
    FROM OPENJSON('["' + REPLACE(REPLACE(@String, CHAR(13), ''),CHAR(10),'","') + '"]') J
    WHERE J.value LIKE 'T-M%'
) S
WHERE RowNum = 20

value	key	RowNum
T-M123-1234567907	48	20