TL;DR => Encrypt files using password and 1+ FIDO2 security keys. The process is quantum-safe and guarantees 256-bit security (due to FIDO2 spec).
This C library (with C++ bindings) provides hardware backed (FIDO2) security for encryption keys in addition to a traditional password. The user typically enters a password to unlock the FIDO2 details, and then uses a FIDO2 key (from a set of N keys) to generate a "hmac-secret" that unlocks the "root" secret (whose security-level is determined by the "seed" but never more than 256 bits). The process only uses quantum-safe primitives, and does not require storage on the FIDO2 key (it does not use a "discoverable" key slot). The security level of the process (that encrypts the "root" secret) is guaranteed ~256-bits, as the FIDO2 spec provides 256-bits of "hmac-secret" material from an internal device/hardware private key mixed with a 256-bit FHSE provided salt (that gets encrypted with password).
The primary drawback is that a metadata blob must be stored along-side the data to unlock the "root" secret. This issue, and lost/damaged FIDO2 keys, is mitigated by providing recovery from a "seed". The seed process is left to the client and is capped at the 256-bit security level; an empty seed can be provided to indicate the generation of a randomized 256-bit "root" secret, which means nothing is recoverable if the FHSE data, password or FIDO2 keys are lost.
The primary use-case is Monero software wallets, where the wallet provides a single seed to the user for recovery. The raw wallet seed is given to a cryptographic-KDF, and whose output is provided to FHSE as its seed. If the user loses their FHSE file, FIDO2 keys, OR password, the original "root" secret can be recovered from the Monero wallet seed. The advantage is that the user can safely store wallet metadata files "in the cloud" with guaranteed 256-bit quantum safe security. The user can also omit the FHSE file from the backup; if the cloud provider steals a FIDO2 key, they still need the FIDO2 salt which is encrypted with password and whose encrypted value is never stored in the cloud. The Monero wallet "keys" file is also encrypted with guaranteed 256-bit security, and does not need to be backed up since it can be recovered from wallet seed.
Hardware wallets (Ledger and Trezor) support FIDO2 standard, but do not allow recovery from seed as there is no way to get secret material without a FIDO2 handle. In other words, the "seed" given to FHSE must be random bytes when using a Hardware wallet. This requires backup of the FHSE file, negating some of the security of the cloud-backup case. Trezor wallet owners can mitigate this by generating a seed from an email address (see macer).
Using FIDO2 to lock wallets provides a more clandestine approach to security - Ledger/Trezor are known cryptocurrency wallets whereas a Yubico device is cheaper and draws less attention.