You install tons of graphics mods and now your game runs like crap. Luckily, there are things you can do to fix it, or at least improve it. Complete improvement is not guaranteed, but these things are worth trying.
Of course, upgrading your computer is an option. In no way do we recommend spending this type of money if you are not in a financially comfortable situation, but if you have a flexible budget, it might be worth looking into. This is a Skyrim modding guide and not a PC guide, so this section will be brief.
The first thing you should look into for PC upgrades is storage. The switch from a hard disk to a Solid State Drive (SSD) or SSD to NVMe is incredible. Everything will load noticeably faster and with minimal stuttering. Secondly, your graphics card, or GPU, while easily one of the most expensive parts of your PC, will cause drastic differences. Of course, it's also worth investing in more/faster RAM and a higher-end CPU. Again, this isn't the guide for PC hardware, but if you have the money then it's something to think about.
There are a lot of misconceptions about texture resolution, so let's clear some things up.
First of all, it is important to understand that models are not flat, and textures are wrapped around them. This means that if you installed a 4k texture, you will not see the entire 4k texture. Because of this, the resolution of your monitor barely makes an impact on the resolution of the textures in your game.
You should pick textures based on the size of the object. For example, you should use 4k or even 8k textures for large things like mountains or dragons. For larger objects and architecture, you can stick with 4k or 2k. For armor and skins, you can stick with 2k, and for tiny objects, 1k is fine.
If you do screen archery or have a lot of VRAM, you can of course install higher-resolution textures. Generally, texture resolution does not have an impact on performance unless you're running out of VRAM.
In our ENB guide, we mentioned that they eat up the largest chunk of your performance, with some presets taking up over half of your FPS. All ENBs can be toggled (Shift+F12 in most cases) if you only want to use it in certain situations, or you could just avoid it entirely. Although we recommend at least trying ENB, our guide touched on ReShade as a lightweight (albeit considerably less powerful) option. Play around with it, and try different presets before completely ditching ENB, as some are more lightweight.
If you followed this guide then BethINI should already be installed and configured. If not, refer to the setup & workspace page. In BethINI, tick "recommended tweaks", and then the medium or low preset. Disable VSync, and enable borderless windowed mode.
In the detail tab, lower the decal quality, godrays, and shadow quality. In the view distance tab, turn down object fade, actor fade, and grass fade.
In SSEDisplayTweaks.ini, change the following:
#Fullscreen=false to Fullscreen=false
Borderless=false to Borderless=true
BorderlessUpscale=false to BorderlessUpscale=true
#Resolution=1920x1080 to Resolution=[YOUR MONITOR RESOLUTION]
#ResolutionScale=0.75 to ResolutionScale=0.9
Remember to remove the # so the setting works. Credit to ChunkeeMunkee for these recommendations, as mentioned in FG's performance guide. However this cannot be used in conjunction to Skyrim Upscaler, as it causes visual distortion.
Essentially how it works is it runs your game at a low resolution and then uses AI to upscale it, causing a massive performance increase with little visual difference. Skyrim now has support for this technology. Refer to the video or mod page for installation instructions.
The video is slightly dated, so you now have to get the base plugin from here, and then download whatever DLLs you need, linked on the base plugin's mod page.
DLSS is for NVIDIA GPUs, FSR2 is by AMD, and XeSS is Intel's take. You can use FSR2 and XeSS on NVIDIA GPUs, but if your card is compatible, DLSS is the best option.
The version of skyrim upscaler compatible with ENB is on the author, Puredark's patreon. However there is ENB Anti-Aliasing which brings the upscaling technology to ENB as well. Make sure to read the description for usage information.
These upscaling methods will only work with DX12-compatible GPUs (NVIDIA GTX 10-series works, just make sure your drivers are up to date), however, DLSS will only work on GPUs with tensor cores (NVIDIA RTX cards). Old cards will have to stick with TAA, which is included with Skyrim (activate in BethINI).
Skyrim Priority SE AE - skse plugin (read the description for CPU affinity alongside priority)
NVIDIA Reflex Support (if you have an NVIDIA GPU)
eFPS - Exterior FPS Boost (make sure you download the official patch hub, unofficial one, as well as the AE add-on if you have AE/CC content)
Skyrim Project Optimization (also requires a few patches)
Additionally, here is a more "up-to-date" guide. Read the guide and it's sub-mods carefully, and check the posts tab: Free FPS.