making a bend allowance calculator

I think Excel can do most engineering calculations (even if it is not always the best tool for the job). How much of your question is engineering (how does anyone anywhere using any programming language or pencil and slide rule calculate bend allowance), and how much is Excel specific (how does one enter the formula(s) for bend allowance into Excel)?

If you already know the formula(s) for bend radius, help us understanding the engineering calculation, and we should be able to help you put that calculation into Excel.

If this is more of an engineering question, I'm not sure that we have any ME's on the board who can help with the engineering. I put "sheet metal bend allowance" into my favorite internet search engine and (among other pages) found this page (https://ncalculators.com/mechanical/...calculator.htm ) with a relatively simple equation for bend allowance.
BA=A*(R+K*T)
where BA is bend allowance, A is bend angle in radians, R is bend radius in meters, T is material thickness in meters, and K is a material specific "fudge factor". I know nothing more about this, or even if this is the calculation you are looking for.
If this is the correct formula, this should be fairly straightforward to put into Excel. You would probably need a lookup table to get the K values (maybe this is where you would use a dropdown list). The other variables should be able to enter straight up. I don't know if you want to include programming for various unit conversions (enter bend angle in degrees instead of radians or thickness in mm instead of m). Those unit conversions should be straightforward (see the CONVERT() function and/or the RADIANS() function).

A lot depends on exactly what help you need. If you need help with the engineering, you might seek an engineering help forum. If you already have the desired bend allowance formula(s) (or once you get them), we should be able to help you put those formulas into Excel.

I am not sure how it would work, either, because I am not sure how you should be calculating bend allowance. That's the engineering/science part of the question I alluded to in my previous post. Help us understand how one should calculate bend allowance, and we can help you program that calculation into Excel. A couple of observations:

1) Assuming the formula I found on the internet is representative of the calculation you want to perform, the formula I gave calls for "bend radius" as well, but I don't see "bend radius" in your screenshot. Does your calculation for bend allowance not require bend radius?
2) It appears that you are having your inputs be number-unit text strings. I would strongly encourage you to enter the values as numbers only, and put any units text in the column header:

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I learned very early in my spreadsheet education that I hated using text manipulation functions to extract numbers from number--unit text strings for calculations. I decided very early to have only one piece of information in a cell (number + unit is 2 pieces of information).
3) Using the formula I found on the internet as an example, it looks like you intend to enter the data in "non-standard" units (as defined by my function), so you will need to consider unit conversions. You can either multiply degrees by PI()/180 or use the RADIANS() function to convert from degrees to radians. You can multiply mm by 1E-3 or use the CONVERT() function to convert from mm to m. One possible advantage I see to using the CONVERT() function is that, if you are ever called upon to work with someone from one of those backward nations (like the US) where they still use inches and feet, it is a simple edit to the CONVERT() function (change "mm" to "in") to allow you to enter numbers in inches.
4) With those observations made, and using the formula I found on the internet as an example, and assuming that you put bend radius in column E (so BA is in column F), the formula for bend allowance might be =RADIANS(C2)*(CONVERT(E2,"mm","m")+VLOOKUP(A2,K_factor_table,2,FALSE)*CONVERT(B2,"mm","m")) I obviously assumed that you will have a lookup table for the K factor (assuming your version of Bend Allowance uses a material specific fudge factor that needs to be looked up) which is not shown in your screen shot.

Those are some programming considerations I suggest you consider. As I indicated, it is difficult to be more specific without knowing exactly how you intend to calculate bend allowance, but that should show you the programming considerations I would expect to encounter.