I downloaded the mod to test it, but it gives an error when are loading.

Hm, enabling this mod by itself (which enables all of the related train vehicle mods), appears to work fine, as well as enabling it alongside either the vehicle grid or grid customizer mods.

There might be some non-default settings affecting your loadout, or there is another mod (unrelated to this pack) causing an issue with one of the other train mods, but the pack definitely works by itself.

This pack is only intended for testing anyways, and whichever other mod is causing the error must have failed the test

I understand that the MOD should run on its own, that's why I disabled everything and just left the base game.
It shows me this error:
2.867 Failed to load mods:
• 5dim_trains
• Missing required dependency 5dim_core >= 2.0.28

Mods to be disabled:
• 5dim_trains (2.0.2)

Your MOD is not activating 5dim_core “5Dim's mod - New Core”

And even if I activate it, it does not work.

Maybe you are using a prototype that is not on the page, please try the one that is on the page.
Download your mod from the page, deactivate everything and activate your MOD (in that order) and maybe then you will see the error that comes out.
Here I can't upload images or the Log for you to see it, maybe there are conflicts between the MODs.

This is not very easy to test, because the mod itself has no other info, apart from the dependencies, which it activates when itself is activated. Deactivating every single mod apart from base is part of my standard testing workflow, so obviously would not fix anything (it's literally what I did to check that it still worked in the first place)

To recreate the conditions from a fresh install, I would need to delete every single related vehicle mod (including 5dims trains and core, which could be the primary cause of the issue, in your case), and then redownload just this mod, to see if it actually downloads all the other mods properly. But other mods with dependencies and subdependencies have all downloaded properly, and there's nothing different about the way this mod is coded that should make that process fail. From a fresh install, that is.

It's possible you already had an older version of 5dims trains? Without having downloaded 5dims core, perhaps by grabbing 5dims trains directly from the mod portal? There are many potential conditions that could lead to this issue, none of which are caused by the modpack itself. I'm not going to delete every single vehicle mod I have, just to debug this one minor issue, especially when there is a very high likelihood of the issue not being caused by this modpack, and which has a very simple fix of just downloading 5dims core manually, and then doing the test again.

The only way I can recreate your error is through a convoluted method of deleting just 5dims core, without deleting 5dims trains, then disabling all mods, and finally reenabling the train vehicles mod. This activates 5dims trains, but does not attempt to download 5dims core (which is a base Factorio thing, and would occur even if you just tried to enable 5dims train, without having 5dims core in the list).

The same error occurs if I delete just 5dims core and the modpack, without deleting 5dims trains. Since the modpack detects 5dims trains, it does not attempt to download 5dims core. But there's no way for the user to have just 5dims trains without 5dims core, unless the user did something weird (downloading 5dims train manually, or deleting a mod as stated above).

I've also tested what happens if you delete all 3 mods: 5dims core, 5dims trains, and the modpack. Then redownloaded the modpack via the in-game mod portal, which downloads both 5dims trains and 5dims core, and it all works as expected. Which leads me to only one conclusion: the issue was caused by user error, or possibly Factorio error, but regardless, not something that can be fixed within the scope of this modpack.

I will reiterate the fix above, regardless of how you got yourself into this bugged state; just manually download 5dims core and it will work.