I've never had any issue reformatting C and keeping D when both are encrypted with bitlocker either on BIOS or UEFI. That video you posted is for BIOS not UEFI install incidentally. What the guy is doing makes no sense. He is destroying the partition table (but not the data in the partitions) and then recreating the exact same layout and then is surprised to contents of the partitions are the same. This is obvious as the data isn't affected. This is nothing to do with bitlocker (or mbr or gpt or tpm) - if you destroy a partition table and make one exactly the same (by whatever method) your data will still be there. He even noticed in the comments that zeroing the disk solves his issue. Don't worry about it - it is not an issue at all.