sum a range until the cell to the left is zero

you could try this
=IFERROR(SUM(INDEX(A2:F2,LOOKUP(2,1/(A2:F2=0),COLUMN(A2:F2))+1):INDEX(F2,0)),0)

Hi, and welcome to the forum.

There's no doubt an array formula but perhaps a User Defined Function (UDF)

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After putting the function above in the VBE at the Module level, in G2 enter

Formula:

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