But it's also another complication since I need to find where to hide this seed. And I think it's already quite difficult to manage the 3 different locations with the 2-of-3 multisig.
Since your goal is to make a cold wallet (you don't make transfers regularly, maybe just once a year or so), I think you have to bear with this backup activity. At the end of the day, security is your goal. I'd encourage you to think hard to find where and how you should store those backups. There are many good threads around this topic, for example, this one[1]. If you want to read more, just search "seed backup" on this forum.
The desktop of the 2-of-3 is not airgapped, it's a "normal" computer, used for all other things. Each element of the 2-of-3 vault has its own weak point (the hardware wallet is the stronger element, though), sure:
The desktop can get a virus and be stolen, as well as the mobile phone.
Consider using an air-gapped device as part of your setup. While the chance that both your phone and PC got compromised at the same time is low, I'd consider them as one of the risks that need to be solved. You can buy a cheap phone and use a live OS to set up your multi-sig, for example. There are obviously some risks regardless of what method you choose, but I think using a daily PC is not that great if you want to set up a cold wallet. CMIIW.
[1]
https://bitcointalk.org/index.php?topic=5263482.0