Mold Earth can maybe create cover in D&D 5e, but it depends on your DM. A forgiving and rational DM would understand the logic behind the reasoning. However, it all comes down to how you explain your usage of Mold Earth, and how strict the table is. Some DMs allow Mold Earth to create a full cover, while some only allow 3/4 of protection. Some stricter DMs do not even grant that privilege.