Generate your passphrase the same way as you did for your seed. Use 7-8 words for it. All lowercase, no spaces

I will try TailOS again. I've downloaded it before, but I got stuck and was never able to get it running. I'm more motivated now to get it working

You need to flash the tails .iso onto your USB stick. If you have an android phone, you can download tails and then use the 'EtchDroid' app to flash the .iso into the USB stick (you may need a USB-C to USB-A converter unless you buy a USB-C or twin head memory stick). Tails comes with Electeum wallet preinstalled. There are no concerns about Electrum. If you use a STRONG and long passphrase that is safe from a dictionary attack, you are also protecting against bad random number generation by the OS.

Solid opsec, now let's get your diet in order with some red meat