How does a hardware wallet interact with the bitcoin network? I tried to understand the principle how the hardware wallet sends transactions to another Bitcoin address since it is not connected via full node to the blockchain.
I found this answer: How do hardware wallets communicate with the outside world?
Do I understand it right that every hardware wallet company like Ledger, Trezor or Shiftcrypto run a full node (e.g. bitcoind) in their company network and every hardware wallet, which is connected via the locally installed company's software at the sender's computer just sends a request to this full node like this?
bitcoin-cli createrawtransaction &quot;[{\&quot;txid\&quot; : \&quot;mytxid\&quot;,\&quot;vout\&quot;:0}]&quot; &quot;{\&quot;myaddress\&quot;:0.01}&quot;

If so, do companies run it's own (closed source) full node which works in a different way? The only exception seems to be BitBoxBase from ShiftCrypto, which is open source.
But basically, the principle of the transaction handling between the hardware wallet and the blockchain is always the same, right? So every company run it's own full node. Only the transmission &quot;protocol&quot; between the hardware wallet and this full node is different and non-standardized, right?
No.
The hardware wallet company sometimes runs a node, but you could just as easily use a client like Electrum instead, and use Electrum nodes instead with your hardware wallet. All the node is used for is checking for transactions and publishing transactions.
The wallet software will use the xpub from the hardware wallet to check for payments people have sent to your addresses, using one of these remote full nodes.
Now, let's say you received some Bitcoin and you'd like to spend it. Your wallet software will generate an unsigned transaction on your computer, then it will send that unsigned transaction to your hardware wallet for it to sign, then the wallet software will use the full node to publish this signed transaction.
So like the answer you linked to pointed out, all the full nodes are used for is 1) querying for existing blockchain data, and 2) publishing (NOT creating) an already signed raw transaction.