A few community members, Luckyone961 and MysticalOS WoW, have posted some possible fixes for FPS improvements for certain content in The War Within.
There are a few known issues with certain WeakAuras and ElvUI settings that can be causing a decrease in FPS performance.
Luckyone961 made a post over on X, formerly Twitter, explaining these issues in detail along with providing steps to help alleviate some of the FPS drops players might be experiencing.
MysticalOS WoW has also posted three videos on YouTube covering the same issues, with tips to help fix them.
For players wanting to improve their FPS issues, here's a few suggestions provided by Luckyone961 and MysticalOS WoW:
Install the BugSack and BugGrabber AddOns to see if any other AddOns might be causing LUA errors.