For high security keys, some systems will export a key by outputting a specified number of “key shards”, which is an m of n set of secret values that are given to five (or however many n is) parties to independently store. When it comes time to recover the value, at least three (or however many m is) people must get together with their shards to decrypt it. This is how a HashiCorp Vault’s master key is set up. It's a classic implementation of Shamir's Secret Sharing.
Other systems use three key-length values that must be XORed together to recover a Key Encrypting Key (KEK); the KEK being used to encrypt the high security key. The KEK is exported as three parts that are printed on paper sheets; the pages are each sealed in tamper evident bags and kept in independent safes, and must all be brought back to recover the secret key. This strategy is often used for distributing a key on paper, sending the pages to three different recipients at three independent addresses via three different couriers. If any of the bags show signs of tampering, the keys are discarded before being placed in service.
Generally, these key parts are long strings of hex values, and are hard for people to enter correctly, or to know when they’ve made a mistake. It’s common to print a Key Check Value (KCV) along with each key part. A KCV serves as a six-digit checksum to help the people who are typing in these long strings; any mistake in data entry turns up as a completely different KCV value.
Finally, some keys are so sensitive that they are generated and stored in FIPS-compliant Hardware Security Modules (HSMs), which are specially constructed to prohibit their keys from being exported. HSMs are often used to store the KEKs for other security systems, such as the master keys for a key management system, a Trusted Root CA's private signing key, the unseal keys needed for a vault, etc. Instead of paper backups, a second (and/or third, fourth, or fifth) HSM is used as a dedicated backup system. This backup HSM is kept offline in a safe, and is only trotted out to make the occasional backup or recovery. A backup HSM can only restore its KEK to an authorized replacement HSM. Such systems are usually proprietary and vendor dependent.