I work on sql server 2017 i need to ask
are separate update will be best or do all update on one step ?

so using only one update to update all columns
or
using only one update for every column update ?

What I have tried:

UPDATE  TT
           SET     TT.strSubstances = CAST (STUFF(( SELECT ','+ CAST(CC.Substance AS VARCHAR(3500))
                                                    FROM   Parts.ChemicalProfiles CC with(nolock)
                                                    WHERE  CC.ChemicalID = TT.ChemicalID
                                                    ORDER BY CC.Substance
                                                  FOR
                                                    XML PATH('')
                                                  ), 1, 1, '') AS NVARCHAR(3500)) ,
                   TT.strMass = CAST (STUFF(( SELECT   ','
                                                       + convert(VARCHAR(3500),CC.Mass,128)--CAST(CC.Mass AS VARCHAR(3500))
                                              FROM     Parts.ChemicalProfiles CC with(nolock)
                                              WHERE    CC.ChemicalID = TT.ChemicalID
                                              ORDER BY CC.Mass
                                            FOR
                                              XML PATH('')
                                            ), 1, 1, '') AS NVARCHAR(3500)),
                  TT.strCASNumber = CAST (STUFF(( SELECT   ','
                                                       + CAST(CC.CASNumber AS VARCHAR(3500))
                                              FROM     Parts.ChemicalProfiles CC with(nolock)
                                              WHERE    CC.ChemicalID = TT.ChemicalID
                                              ORDER BY CC.CASNumber
                                            FOR
                                              XML PATH('')
                                            ), 1, 1, '') AS NVARCHAR(3500)),

                   TT.strHomogeneousMaterialName = CAST (STUFF(( SELECT   ','
                                                       + CAST(CC.HomogeneousMaterialName AS VARCHAR(3500))
                                              FROM     Parts.ChemicalProfiles CC with(nolock)
                                              WHERE    CC.ChemicalID = TT.ChemicalID
                                              ORDER BY CC.HomogeneousMaterialName
                                            FOR
                                              XML PATH('')
                                            ), 1, 1, '') AS NVARCHAR(3500)),
                                            --strHomogeneousMaterialMass
                   TT.strHomogeneousMaterialMass = CAST (STUFF(( SELECT   ','
                                                       + convert(VARCHAR(3500),CC.HomogeneousMaterialMass,128)--CAST(CC.Mass AS VARCHAR(3500))
                                              FROM     Parts.ChemicalProfiles CC with(nolock)
                                              WHERE    CC.ChemicalID = TT.ChemicalID
                                              ORDER BY CC.HomogeneousMaterialMass
                                            FOR
                                              XML PATH('')
                                            ), 1, 1, '') AS NVARCHAR(3500))
           FROM    #ChemeicalIDCounts TT

OR
DO separate update as below

   UPDATE  TT
            SET     TT.strSubstances = CAST (STUFF(( SELECT ','+ CAST(CC.Substance AS VARCHAR(3500))
                                                     FROM   Parts.ChemicalProfiles CC with(nolock)
                                                     WHERE  CC.ChemicalID = TT.ChemicalID
                                                     ORDER BY CC.Substance
                                                   FOR
                                                     XML PATH('')
                                                   ), 1, 1, '') AS NVARCHAR(3500)) 
            FROM    #ChemeicalIDCounts TT

			 UPDATE  TT
            SET     TT.strMass = CAST (STUFF(( SELECT   ','
                                                        + convert(VARCHAR(3500),CC.Mass,128)--CAST(CC.Mass AS VARCHAR(3500))
                                               FROM     Parts.ChemicalProfiles CC with(nolock)
                                               WHERE    CC.ChemicalID = TT.ChemicalID
                                               ORDER BY CC.Mass
                                             FOR
                                               XML PATH('')
                                             ), 1, 1, '') AS NVARCHAR(3500))
            FROM    #ChemeicalIDCounts TT

etc..