What format is that this pockets saved in?

Background

Some years in the past (2017) I should have discovered a strategy to ‘serialise’ my pockets, as a result of I saved the next in my password supervisor:

• Identify: “Bitcoin pockets”
• Password: (typical generated password)
• Era seed: (BIP39 mnemonic)
• Receiving deal with: (typical bitcoin deal with)
• Notes: (appears like base64 knowledge, about 3000 characters in size)

I vaguely keep in mind having the Bitcoin-Qt consumer put in.

Query

What methodology did I exploit to serialise (or export, or back-up) my pockets in 2017?

Additional info

What I attempted thus far:

• Copied the info to textual content file
• Ran bitcoin-cli importwallet “/path/to/file.txt” (through Bitcoin-Qt’s console). Acquired the error “Solely legacy wallets are supported by this command (code -4)”.
• Decoded the textual content file utilizing cat /path/to/file.txt > base64 -d > /path/to/file.dat and ran bitcoin-cli importwallet “/path/to/file.dat”. Acquired the error “Solely legacy wallets are supported by this command (code -4)”.
• In Bitcoin-Qt chosen File, Restore Pockets…, and chosen the .dat file. Acquired “Pockets file verification failed. Did not load database path ‘~/Library/Utility Help/Bitcoin/wallets/Take a look at’. Information just isn’t in acknowledged format.”
• Ran file /path/to/file.dat and acquired file.dat: knowledge (I hoped it could be recognized as Berkeley DB, since I learn right here that pockets.dat recordsdata are BerkeleyDB database recordsdata).
• Checked the hyperlinks within the reply to this query concerning the ‘pockets export’ format, however it appears like that’s only a strategy to encode a personal key, which might not outcome within the form of knowledge I’ve saved in my password supervisor.

What I didn’t do but:

• Set up the model of Bitcoin-Qt present in 2017, and try to revive the .dat file.