Residential Solar energy credit and Marrried filing separately

I am preparing a 2021 return for a married couple that wants to file married filing separately so that her student loan payments will be less. Yes, I do show them the comparison of tax savings by filing married filing jointly. They purchased a solar panel system in 2021 on their jointly owned home. My question is do you just split the cost evenly and then prepare a separate Form 5695 for each return using 1/2 the cost? Or, when you look at the instructions on page 2 for form 5695 under joint occupancy,

https://www.irs.gov/pub/irs-pdf/i5695.pdf

it talks about the maximum qualifying costs that can be taken into account is $1667 for each one-half kilowatt of capacity of the property which can account to less the the amount paid. It then says the rules don't apply to married individuals filing a joint return.

So, I want to make sure I do an accurate comparison for MFJ vs MFS, but this energy credit is not clear to me.

Any help would be appreciated!

Thanks!