Try these Google sheets formula instead:

=B1 + SUM(BYROW(TOCOL(SPLIT(B8,",")), LAMBDA(r, FILTER(B2:B4,A2:A4 = trim(r)))))

or if you want to multiply each value, use this:

=B1 + PRODUCT(BYROW(TOCOL(SPLIT(B8,",")), LAMBDA(r, FILTER(B2:B4,A2:A4 = trim(r)))))

References:

• BYROW()
• FILTER()