From what I've seen on websites, yes. Just afaik there's more to read about SeedSigner, for example I think that it doesn't work with Electrum (it may do with Sparrow) and you have to generate the seed separately yourself.
I know that it works with Sparrow, Blue Wallet, and some other less-known bitcoin-wallet. I think you are right about the Electrum.
Yeah, the seed has to be generated on the Seedsigner. For example, with dice rolls. There is another option to do it using images you take with the device's camera, but I am not sure how this works exactly. I am sure it's not difficult to learn if it comes to that.