פירוש על ראש השנה 4:1

It is forbidden to eat new (crop) of the five types of grain until the Omer is brought, which is the 16th of Nissan. As it says, “And bread, toasted grain, and unripe (or damp) grain you may not eat until (the end of) this very day.” And in these times that there is no Omer, it is forbidden (on) all of the 16th day. And outside of Israel where we observe two days, it is forbidden (on) all of the 17th day, until the beginning of the night of the 18th.

21. We do not break the laws of Holidays for the Rosh Hashanah shofar, even something that is only rabbinically prohibited. How so? If there was a shofar at the top of a tree or across a river and there is no other shofar, one does not climb the tree or sail on the water. Having a non-Jew do these things is permissible, because that is a rabbinic prohibition on top of a rabbinic prohibition.(Meaning, the prohibition of telling a non-Jew to do an action [on a holiday] that is prohibited by the Torah is a rabbinically enacted prohibition to ensure resting [shevut] from telling non-Jews to do things, and when the action in question is itself a rabbinic prohibition, this is a rabbinic prohibition on top of a rabbinic prohibition [shevut d'shevut]) and when there is a commandment to do, the rabbis made no such decree (see 307).

5. If the holy day of Rosh Hashanah falls on Shabbat we do not sound the shofar. Rema: and it is even forbidden to handle a shofar, unless if needed for itself (i.e. in an allowed Shabbos act like to carry water) or it’s place (i.e. on a chair that one wants to sit).