Yeah, I wanted a completely different seed, but it sounds like that isn't going to be very convenient to do. Ah well, I suppose if I ever end up buying a laptop I'll install LL on that and fire up the Nano X. No rush.
It's not impossible... you just need to use a decent naming convention when you are adding the accounts to Ledger Live so that you don't get them mixed up. The downside being that it basically just lumps all the accounts together in the "portfolio" and "Accounts" section... you don't have any option to segregate them by device or even passphrase etc, so depending on your reasons for wanting "independent" devices, this could be a nuisance
Alternatively, as already mentioned, Electrum probably makes it easier to segregate your devices while using "one app", as you simply create a new wallet file within Electrum dedicated to the Nano "X"... and call it "NanoX_wallet" or something similar... and if you choose to encrypt the wallet, it won't even open without the device connected. The downside of using Electrum being that you will only have access to BTC.
In any case, you need LL to be able to install/remove/update the coin apps and any firmware updates etc.