Part 1:

Yep. The Deck and SteamOS have Secure Boot.

I never said they did not.

I said:

The Steam Deck does not officially support Windows Secure boot.

Because…

Basically, Secure Boot means that … no other OS is allowed to boot.

That’s what ‘Secure’ means, to Windows/MSFT.

Not sure if you struggle with reading comprehension in English, but when you read all of this, together, it is obvious that I am saying that the Windows specific implenentation of Secure Boot is exclusionary, only works with Windows.

This is true, by default, unless you do a bunch of other extra work, which is easy to fuck up and likely to fail at some future point, because the way Windows ‘does’ Secure Boot is very different from how basically every other OS does, and will constantly change in subtle and esoteric ways that often result in a user being unable to access any other OS than Windows.

Windows Secure Boot is thus functionally a distinct thing, even if Windows/MSFT act otherwise and insist on confusing and obfuscatory terminology… which they have a long track record of doing with basically all of their software and related nomenclature, for decades.

Part 2:

Yep, which is why I described that in layman’s terms by saying:

maybe unless you have literally physically distinct harddrives/ssds/microsd/usb drives that each OS lives on?

And then do extra steps to tell your now Windows managed BIOS/UEFI that your linux dual boot OS is also ‘safe’ for Windows to allow your sysyem to boot?

Yep, you can do some extra bullshit, and it might work for a while, untill a new Windows update of some kind rewrites your UEFI config, requires some new arcane dependency setting or config of some kind, which then will lock out your non Windows OS.

Yep, other Mobos often come with everything preconfigured for Windows and their specific implenentation of Secure Boot.

The Steam Deck doesn’t, and that is what we are talking about.

Also, its entirely possible and even common for dual boot and linux users to either intentionally or unintentionally wipe out those Windows EFI files, alter the cryptographic signing process in some other way, and then you run into this same problem on other Mobos.

Or if you just build your own PC, or a linux oriented laptop or PC, Mobo will not come preconfigured for Windows.

No problem!

Yeah, dual booting Win and Lin is… basically a trap at this point, I first tried to do it over a decade now…

There really is no need anymore, beyond very specific uses cases, to run Windows at all.

Linux caught up and has now exceeded it in basically everyway, as Windows has also enshittified.

I would suggest you look into just switching your Deck over to Bazzite.

From a basic user stand point, it is highly functional and performant, harder to break than Arch based SteamOS if you make it not read only, gives you more flexibility and utilities than default SteamOS, and you can even set up a linux container as a dev environment to do linux dev stuff, use Bottles or something if you need something closer to a Windows environment.

Yeah, its still not gonna play those few, super hyped and marketed AAA games… but fuck em, they’re evil corpos, stop giving them your time and money.

…

And I just made another suggestion to you in another comment:

You want BF style game(play)?

TitanFall 2. Still alive, still alive, got a reverse engineered launcher, server browser and private servers, runs great on linux via Proton.