How to fix old games being run in portrait mode on the Windows tablet

There is an interview with Boris Schneider-Johne from Microsoft explaining why old games won't run on Windows 10.

“Everything that ran in Windows 7 should also run in Windows 10. There are just two silly exceptions: antivirus software and stuff that’s deeply embedded into the system needs updating – but the developers are on it already – and then there are old games on CD-Rom that have DRM. This DRM stuff is also deeply embedded in your system, and that’s where Windows 10 says “sorry, we cannot allow that, because that would be a possible loophole for computer viruses.” That’s why there are a couple of games from 2003-2008 with Securom, etc. that simply don’t run without a no-CD patch or some such. We can just not support that if it’s a possible danger for our users. There are a couple of patches from developers already, and there is stuff like GOG where you’ll find versions of those games that work.” (translated by Rock, Paper, Shotgun)

It's hard after that to counter Microsoft in their decision. As he said, you can buy an other digital copy that works on Windows 10, but I know, it's not really nice to buy something we already have. Sadly, this is the easier solution. Steam is selling every games you mentioned in your question. However you can try solutions below, but it requires some specific knowledge and may take time to set up.

The first alternative solution is to dual boot your computer with an older Windows version that can install and run your games. Each time you'll boot your computer, you'll have the choice running Windows 10 (daily usage) or Windows 98 (for games). Here's a second example setting up dual boot.

Finaly, you can try to install a virtual machine with an older Windows version and play the games, but it will not handle your full PC performance and there is risks that may not work correctly.

--EDIT--

As mentioned in comments, if you're able to install the game but unable to launch it, you can apply a no-cd patch.

I would say to need to have the Xbox Application (XboxApp), since that will make it easier to launch games. Games that install on your computer get buried deep within folders as I've found out. Gears of War 4 for example was within a very messy folder structure. I'm not even sure if it was possible to launch the game without the app.

XboxIdentityProvider is likely needed as well. This site states its description:

The description says : "A system app that enables PC games to connect to Xbox Live."

Here is the link to redownload the identity provider. You won't be able to connect to Xbox Live if you do not have this downloaded.

You should be able to get away with not having the XboxSpeechToTextOverlay, which at the moment, appears to only be available for one game (Halo Wars 2). According to that site, this service provides:

...a speech-to-text service that also supports text-to-speech.

I assume games will work fine without this - Halo Wars 2 may be the only game impacted by it for now if anything.

The XboxGameOverlay I believe is the service that controls the feature when you press the Windows Key + G. The first result after Googling it yields this article about how to disable it. You should be fine without this, but note that taking screenshots and recordings with this service allows you to share it to Xbox Live (using the above mentioned Xbox Application). Without it, you won't be able to share your content to Xbox Live - or at least not as easily.

Bonus:

Reading this Microsoft Help article, if you are signed in with a local account:

Upon launching any Microsoft app, including the Store, you'll see a prompt to sign in or create a Microsoft account. The first Microsoft account you use to sign in will become the default account your device will use to sign you in across all Microsoft services.

If you are using a local account to sign in to your PC, you will need to use a Microsoft Account to use any Microsoft Applications (including the Xbox Application).

If you use a Microsoft Account as your PC login:

If you signed in to Windows 10 using your Microsoft account, that account will be linked to the user account signed in on the PC. This makes it much easier to sign in to all Microsoft apps (Skype, OneDrive, Office 365, Xbox, Groove Music, Movies & TV, and much more).