=filter(Planning!G$5:G$37; regexmatch(Planning!G$5:G$37 ; "![a]"))

=filter(Planning!G$5:G$37; regexmatch(Planning!G$5:G$37 ; "<>a"))

=filter(Planning!G$5:G$37; regexmatch(Planning!G$5:G$37 ; "a"))

=FILTER(Planning!G$5:G$37; NOT(REGEXMATCH(Planning!G$5:G$37; "a")))

=FILTER(Planning!G$5:G$37; NOT(REGEXMATCH(TEXT(Planning!G$5:G$37;); "a")))

=FILTER(Planning!G$5:G$37; NOT(REGEXMATCH(TEXT(Planning!G$5:G$37;); "a")) * LEN(Planning!G$5:G$37))

=FILTER(Planning!G$5:G$37; NOT(REGEXMATCH(TEXT(Planning!G$5:G$37;); "a")), LEN(Planning!G$5:G$37))

=QUERY(A1:A10, "where not A contains 'a' and A is not null")