LIKE is a "wildcard" search, similar to a file list "*.txt" finding all files which have a text extension. So when you use
dv.RowFilter = "[ColumnOne] LIKE 'AB,AD,AZ" + combobox1.Text.Trim() + "%'";
It looks for a row that has a column that starts with "AB,AD,AZ" and your combobox content - not match any one of them.
SQL doesn't support regex-style comparisons, so if you want to separate strings starting with "A" from those starting with "Z" you will have to be explicit about it:
string selector = combobox1.Text.Trim();
dv.RowFilter = "(" + selector + " = 'Luft' AND LEFT([ColumnOne],1) = 'A' ) OR (" + selector + " = 'Bus' AND LEFT([ColumnOne],1) = 'Z' )";