integrating Electrum with Ledger Nano S

[dkbit98]

Imagine if one day electrum doesn't exist anymore their servers are down and you are stuck with their unique seed words format...

The same could happen to the Ledge servers or they have a general seed words format that I can use with other wallets?

Ledger wallet is using standard BIP39 for generating mnemonic seed and you can import this in most other hardware and software wallets including Electrum.
Servers can go down but you always have seed words and you can use full node and other wallets.

Please recommend me a good book or video course about Bitcoin.

I have no idea about books but you can start reading Bitcoin whitepaper and watch anything from Andreas Antonopoulos on youtube:
https://www.youtube.com/c/aantonop/videos

[Lucius]

The same could happen to the Ledge servers or they have a general seed words format that I can use with other wallets?

Accounts generated by a Ledger Nano S device can be recovered on any (third-party) hardware or software wallet that supports the same standards as Ledger (BIP32/BIP39/BIP44).

In other words, if Ledger as a company disappears one day, there are quite a number of alternative crypto wallets with which you can gain access to your coins. I quote only one sentence, but everything is explained in detail on the link above.

Please recommend me a good book or video course about Bitcoin.

I suggest you start your research from here -> https://bitcoin.org/en/