Apologies @Hnasir1231 I may be a little confused are you asking for the the dropdowns to come together and create a combined string but be a star if blank? if so that would be this:
If(IsBlank(Dropdown_BM.Selected.Value),"*",Dropdown_BM.Selected.Value)&"-"&
If(IsBlank(Dropdown_BBBSize.Selected.Value),"*",Dropdown_BBBSize.Selected.Value)&
If(IsBlank(Dropdown_LN.Selected.Value),"*",Dropdown_LN.Selected.Value)&
If(IsBlank(Dropdown_H.Selected.Value),"*",Dropdown_H.Selected.Value)&
If(IsBlank(Dropdown_B.Selected.Value),"*",Dropdown_B.Selected.Value)&
If(IsBlank(Dropdown_GB.Selected.Value),"*",Dropdown_GB.Selected.Value)&
If(IsBlank(Dropdown_Base.Selected.Value),"*",Dropdown_Base.Selected.Value)&
If(IsBlank(Dropdown_Pfrm.Selected.Value),"*",Dropdown_Pfrm.Selected.Value)&
If(IsBlank(Dropdown_LC.Selected.Value),"*",Dropdown_LC.Selected.Value)&
If(IsBlank(Dropdown_ECO.Selected.Value),"*",Dropdown_ECO.Selected.Value)&
If(IsBlank(Dropdown_FP.Selected.Value),"*",Dropdown_FP.Selected.Value)&
If(IsBlank(Dropdown_TD.Selected.Value),"*",Dropdown_TD.Selected.Value)&
If(IsBlank(Dropdown_Bdwn.Selected.Value),"*",Dropdown_Bdwn.Selected.Value)&
If(IsBlank(Dropdown_RA.Selected.Value),"*",Dropdown_RA.Selected.Value)&
If(IsBlank(Dropdown_Cmp.Selected.Value),"*",Dropdown_Cmp.Selected.Value)
If that is not what you wanted but you wanted something different could you please explain it again for me alternatively we can call on teams to discuss if needed