Is the prohibition against performing Melacha on Chol Hamoed Biblical or Rabbinical?

It is disputed amongst Poskim whether the prohibition of doing Melacha on Chol Hamoed is of Biblical or Rabbinical origin. Some Poskim[1] rule it is Biblically forbidden. Other Poskim[2] rule it is Rabbinically forbidden. Practically, Admur rules it is Biblically permitted to perform Melacha on Chol Hamoed and it is merely Rabbinically forbidden to do so.[3] Nevertheless, the Sages stated that one who belittles the Moed does not have a portion in the world to come and it is considered as if he has served idols. Hence, one must be very careful in the laws of the Moed, even though they are considered merely Rabbinical in nature.

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[1] M”A 530:1 and Beir Hagoleh 530 that so is opinion of Beis Yosef; Rashi; Rashbam; Ramban; Ritva; Rabosav of Yireim; Meiri in name of many Geonim; Rif; Sefer Hachinuch; Shivlei Haleket; Eshkol; Ritz Geius.

[2] Rabbeinu Tam Tosafus Chagiga 18a;; Riva; Rambam Yom Tov 7:1; Smag; Bahag; Rosh; Nimukei Yosef; Riaz; Meiri; Rid; Rabbeinu Gershom; Or Zarua 1:589; Orchos Chaim; Tashbatz; Tur 530; Kol Bo; Shulchan Aruch Harav 31:2

[3] 31:2