Is Electrum still safe to use?

It's help window says it connects to a single server to get your transaction history, and I assume that server is backed by a single Bitcoin core node.

In addition, its help says it connects to several nodes to get the headers and uses them to verify the transaction history sent from the single server.

Even if the server and all nodes a wallet uses were compromised I can't think of a way your Bitcoins could be at risk of theft if you sign Electrum transactions offline, and only transmit them through a watching only wallet connected to the internet.