@RyanThomas - I took the liberty of taking a look at your App, and I have some feedback/suggestions for you.
Firstly, you have non-User Specific Columns in your Beam Calculator table. Assuming that you intend to have more than one user of your App, then this will cause you problems. When you have two or more users interacting with that screen at the same time, every time one makes a selection, the selection will change for all the others. User Specific Columns address this problem, as it allows each user to have their own version of the data in the same column/row.
So you need to change the following columns:
Secondly, you have redundant data in your tables. What I mean by this is that you have a Lighting Fixture column in your Lighting Units table, and then another column for Lighting Fixture in your Lighting Unit Configurations table. You then use those in a relation between the two tables. Using item names in this way to form relations is not recommended, because of its fragility. Names can change, and when they do, things will break. For example, there are two rows in your Lighting Unit Configurations table that have no matching row in your Lighting Units table. Row 41 (600D Pro) - maybe that should be Aputure 600D Pro?, and Row 63 (Litemat Spectrum), which I’m guessing should be Litemat 4 Spectrum?
A better approach to this is to create a single source of truth for your Lighting Units, and have everything else refer back to that. Then if you ever need to change a name, it only needs to be changed in one place, and nothing will break.
The way to do this is by adding a RowID column to your Lighting Units table, and use that as a LightingID in other tables. So in your Lighting Unit Configurations table, instead of storing the unit name, store the UnitID. If you need the name in that table, all you need to do is create a relation matching the UnitID with the RowID column in the Lighting Units table, and then use a lookup column via that relation.
Just getting back to your original question, the way I would deal with that is to use the selected Fixture to build a multiple relation back to your Lighting Unit Configurations table, use a lookup column to fetch an array of associated Beam Angles, and then use the state of that array (empty or not) to decide what to display.
Below is a link to a copyable version of your App with the above changes implemented.