Recent releases of bitcoin core are hierarchical deterministic (HD) wallets, and you can use the HDSEED to backup and restore the wallet.  An easy way to obtain your HD seed and back up several private keys (including imported ones) all at once is to use dumpwallet.  That will create a clear text file with a bunch of your private keys and associated addresses, but one key is of particular importance; it'll be labeled "hdseed1."  It's a WIF private key, and it can be used to restore a bitcoin core HD wallet with all the other addresses and change addresses.  It will not restore any private keys that were imported using importprivkey or importmulti.

Generally speaking I shy away from storing my backups digitally.  I don't trust the archival longevity of digital media.  The backups I trust most are seed phrases written on paper.  A private key or a QR code on paper is also extremely robust, in my opinion.  The most important thing, however is redundancy.