Test if contents in one cell exist inside a different multiline cell

Hello all, I am a mechanical engineering intern doing stuff in excel so forgive me if this is super simple. I have a file with about 2K lines of code to do various things like compare files, highlight differences, check for similarities etc.

I am running into an issue with an expansion of functionality that is being requested. In the original files each cell only had 1 string of data in each cell so my comparison tool essentially did

Please Login or Register  to view this content.

I am now being given a file with multi lines of text. I have attached an example folder but the gist of what I need is this.
I have a set of data and on a different sheet a dependent drop down filter. The user selects the data to filter through and the filer program goes through each line in the appropriate column on the data sheet and brings it over to the filter sheet. I have code for everything except how to get the filter to look through each line in the multiline cell as a separate line
if someone has an idea for code that would be similar to

Please Login or Register  to view this content.

I have no idea in this pseudo-code how to get the variables linecount or actual_data. If anyone knows how to get those two variables I would appreciate it greatly and believe I can figure the rest of it out from there.

Example file of what I intend to make the final result resemble is here Drop Down Test.xlsm

I'm not sure if I understood correctly but try the following:
Copy and paste this macro into the worksheet code module. Do the following: right click the tab name for your "Filter" sheet and click 'View Code'. Paste the macro into the empty code window that opens up. Close the code window to return to your sheet. Make a selection in cell A4.

Please Login or Register  to view this content.

You are very welcome.