Dropdown dependent dropdown based upon multiple selections.

[jcschafer209]

I would like to create two columns of dropdowns. Dropdowns in M28:M127 and then N28:N127. M is a subject matter selection and N is names. The N dropdowns are meant to be dependent on the M dropdown. However, I want the N dropdown to reference the multiple selections made from the column M dropdown or I want N's dropdown to show all of the names associated with the subject matters chosen from column M. I have a vba code already running that allows for multiple selections to be made and displayed in column M where the multiple selections are displayed(delineated) in M by comma space(at least I think). I want N's dropdown to show all of the corresponding names based upon the multiple selections made in M's dropdown. The dependent dropdown in N works with one dropdown selection but not multiple. I was using this formula as to be referenced by N's "Source:" validation and it worked but only for one selection.
=UNIQUE(FILTER(Table6[Subject Matter Area(s) of Interest
(Requires Input)],(Table6[Subject Matter Area(s) of Interest
(Requires Input)]<>"")))
tried to modify it to this...via copilot's suggestions and ended up with "#CALC!"
=IF(M28="", "", UNIQUE(FILTER(Table6[Name - Person with Interest
(Requires Input)], ISNUMBER(SEARCH(TRIM(MID(SUBSTITUTE(M28, ",", REPT(" ", LEN(M28))), (ROW(INDIRECT("1:" & LEN(M28) - LEN(SUBSTITUTE(M28, ",", "")) + 1))-1)*LEN(M28) + 1, LEN(M28))), Table6[Subject Matter Area(s) of Interest
(Requires Input)])))))
Also, I'm kind of "brute forcing" my way through this creating multiple dependent dropdowns by creating new unique lists for each and every dropdown in columns M and N. So, I'd like to avoid doing this for an additional 93 times because I would like 100 dropdown dependent dropdowns based upon multiple selections. Any suggestions?