Specifically both KOTOR games and Thief Deadly Shadows.

Is there any way to make them 1080p particularly without the use of mods, or I have to use mods?

Because I made games like Deus Ex and Doom 3 run in 1080p without mods, but I can't seem to do it with these games i listed above.

There should be a way (don't remember it though), but expect everything to be stretched and extremely small as those games were made for 4:3 resolutions. I remember forcing KOTOR into 1080p somehow and it was pretty bad. Unless someone made a mod that actually re-scales the UI elements, texts and adjusts the FOV, I would not recommend it.

You can always try DxWnd and see if it can launch them. You can set any resolution for the games that way and much more. But you need to set the games up properly in it.

Have you tried suggestions from PCGamingWiki?
https://pcgamingwiki.com/wiki/Home

Edit: oops, missed the without mods part...

The site claims this is still in beta (i.e., not ready for general use) so beware you might need to tinker and also it is expected any problems will be sent back to the developers for incorporation into the completed build. The Gaming Wiki is a terrific resource that we all should promote. Thanks! :)

You can mod KOTOR to run at different resolutions (I'm assuming 1080 included), or you can use this, which also works for a list of other games: https://flawlesswidescreen.org/


Edit: I used FW to play through KOTOR the first time round and it did the job well.

What about Thief Deadly Shadows?

If I had an answer for that, I would have posted it.

As always, check the subforums.

I just worry that me modding the game's resolution and aspect ratios and what not might cause the game to crash for me even if I follow instructions to a tee.

Especially since these games have built in pre-rendered cinematics that default to their own resolutions.

I know you said "no mods", but I strongly recommend you use Sneaky Upgrade for that one. Some games work with 1080p with no mods due to storing resolution data in .ini files, but others need changes to the renderers / modding to do so. Sneaky Upgrade fixes up some bugs / crashes, can add Borderless Windowed Mode, and is highly tweak-able as to how much / little you want to change. I've never had any problem with it.

What I find weird is that Thief Dark Project and Metal Age both support 1080p right out of the box as an option in-game.

But not the latest sequel in the series?

At least this particular console port gameplay wise plays better then Deus Ex Invisible War ;)

Both Thief 1 & 2 (and System Shock) have been pre-patched by GOG with the NewDark patch (aka TafferPatcher / TFix) also made by modders based on the TTLG forum. The original retail disc version of Thief 1-2 didn't support widescreen and had one or two annoyances like the map was at a fixed resolution different to the game so viewing it in-game caused the monitor to blank out for 1-2s whilst it changed resolutions. NewDark patched a lot of things inc adding widescreen, removing CD checks, upgrading renderer from DirectX7 to 9, FOV control, adding Bloom, etc.