=LET(work;Filter(
    IMPORTRANGE("https://docs.google.com/spreadsheets/d/1MPCIXoBqguYu9oRnwQ2tfYMqY_vY4tS5dJzNF7by3aY/edit?usp=sharing";"'"&Cell("Sheet";date)&"'!B1:S1");
            INDEX(IMPORTRANGE("https://docs.google.com/spreadsheets/d/1MPCIXoBqguYu9oRnwQ2tfYMqY_vY4tS5dJzNF7by3aY/edit?usp=sharing";"'"&Cell("Sheet";date)&"'!B2:S40");Day(date))
    =job);
    If(second="--";"Course not possible";
        SWITCH(true;
            COUNTA(work) = 1; "Not enough workers planned";
            COUNTA(work) = 2; TEXTJOIN(", ";true;CHOOSECOLS(work;2));
            COUNTA(work) >=3; TEXTJOIN(", ";true;CHOOSECOLS(work;SEQUENCE(1;COUNTA(work)-2;3)));
        )
	)
)