Before we begin we first need to go over the software we'll be using, Lossless Scaling, which is available right here on steam for free! This software is free but doesn't have access to all the upscaling methods unless you pay $5, which is fine for what we're doing. So now install the demo, giving you unlimited software access with the limited features.
Lossless Scaling On Steam

Im aware that Portal RTX has DLSS, but you either get it to look really good at 20 fps or really bad at 144. To achieve good quality and fast frame rates we will be combining DLSS with Lossless scaling. After you have launched Portal RTX navigate to the video settings and change your resolution. This part is up to you to determine based on your hardware. Lower your resolution and set portal to run in a borderless window.
now tab into Lossless and set your settings to match mine,
After doing this click blue scale option in the top right of lossless and tab into portal RTX. Lossless will scale the focused application after 5 seconds. Now click Alt + X to bring up the nvidia RTX remix settings, here you can change your DLSS settings until you reach the desired frame rate!

Congrats! I hope this guide helped you to be able to play portal RTX with high frames! What we have done is lowed our resolution in portal so that your PC is having to render less pixels than upscaling it to full resolution afterwards with lossless! If this guide helped you please favorite it so you can find it later! And maybe leave an award?...
Good Luck!!