Packaged game wont run on the better GPU

Hey there

I’ll outline the Situation first:
We bought an external case for one of our 3080TIs to run our packaged games on a laptop, which would run bad on them because it only has a 2080.
We’re doing architectural Walkthroughs and want to show them to clients locally.

Most of them take the new GPU linked by Thunderbolt.
There is just one of our games which wont take it whatever we do.
Its an older one that was developed in 4.25, upgraded to 4.27 later and now migrated the levels into a fresh 5.1 as to not get problems with old project settings if i just “updated” the project via Epic Games Launcher.

We tried telling it in the graphi settings to take it.
We deactivated the 2080, it went to Intels internal GPU.
We deactivated that too, now it takes just the CPU, which means it has 30 spf now. seconds per frame.

Than we tried it on other machines in our Office, like mine. Got a 2080TI and a 3080 TI. It took the 2080 of course.

I rebuilt the PC and gave the 3080 the upermost Slot, didnt help.
I asked ChatGTP and it told me a lot of crap that isnt available in UE5 anymore.
I updated the drivers and now the game just upright crashes at start, making the GPU crash with it.

We’re out of ideas.
its a hefty project that run on baking back in the day and we want to present it in all the Lumen glory now, but that needs a 3080ti to run.

try fixing the rendering settings in project settings and keep target hardware to highest if you want game to choose the higher GPU as well as keep engine scalability to cinematic
and then package it