I’ve noticed the framerate has reduced roughly by half since the 9.0.5 update. Places I’d normally get ~60, now I get ~30. Places I’d normally get ~40 now I get ~20. Etc.
This would occasionally happen prior to the update, but resetting the app would solve the issue. No such luck now.
Same here. I am on a M1 Macbook pro. With the same settings prior to the patch, I would get 60fps everywhere with the exception of Ardenweald. Now in Shadowlands, most I can get is 30. Something definitely changed and I can’t figure out what it is.
Check your addons. It’s almost a guarantee they’re firing off so many Lua errors that they’re tanking your FPS. Either update them or disable them until updates are released for them.
For some fokes it is the vsink.
Open Escape or menu then grafics. At right , third down from top. Uncheck it.
Blockquote
Check your addons.
My what now?
I’m too much a filthy casual for addons. 
Turn off V-Sync,
I personally set my resolution down to 1920x1080. with a UI scale of .75
Doesnt look the best, but back to 60-70fps
Mine:
MBP M1, 16-Ram
I’m have same issue, but first I guess are the Addons not update yet, I only run 3-4 addons, also I notice now the recommended settings from Wow, are Settings 2, before I had 5, normally I tuned by my self the Graphs, but I notices some issues while doing my WQ , when I decided to reset my graphs to recommended I notices this issue. what I do since Day 1 is do not use “Default” Resolution is scale to 2880x1880 it eats from 60 (Vsync-on) to 37 or less depends the place. so my settings are:
Resolution: 2046x1280
General:
Environment:
)Effects:
High
Good
Disable
High (I set particles at High because I use the mangoes illusion and looks better here, but this can consume so much FPS also in Ardenweald some spots will be so wavy particles like Mist places, but if doesn’t mind some little details in Good stills great and does not drops too much in Ardenweald)
Disable (SSAO always has consume so much FPS at least from my experience, it makes some objects looks better with shadows, you could turn it at “Low” so you could see some better Shadows/Contrast on buildings and ground. you could see this effect better on the stairs the “Black Lines” on them, or walls the inside corners looks darker)
Disable
Disable (the Outline mode I use it this way because is easier to find Quest objects and herbs, mining spots also Quest NPC)
With these settings I’m 70% of the time at 60 fps, only drops in World Bosses and Maps Spots where Particle Density and some other things, I couldn’t find/see.
And with this resolution the only thing you could see when change from 2.8k is the details on the letters (still readable) and spell icons (become less HD kind of)
Ah! about the V-sync some people had issues with this (also me) if you turn off the V-sync some times it Freeze you could still hear the game and other apps if use it but can’t do anything , nothing respond, at this points you have to Hard-shutdown the Mac, I do not know if this only happen with Mac’s own display or external too.
Thanks for reading until here. hope this help you.
Note: I do not cap my FPS in game only background.
Thanks! Lowering the resolution seems to be the best workaround for now, until they fix whatever went wrong (hopefully soon…)
FWIW turning off V-Sync just made my situation worse; FPS nominally stayed the same, but I ended up losing even more frames. 
This would likely be because unless you have the framerate limiter active, your system was rendering as many frames as it could, generated (much) more heat, and throttled because of it. Unless you have a high refresh rate display (120/144/165/240 Hz), your max framerate should be set to 60, vSync or no vSync.
M1 Mac Mini here running at 1080p, with the graphics slider at 7 and shadows set to “low”, particle density set to “good”.
FPS hovered 60 fps almost all the time, now that’s not the case. Experiencing fps drops in places that weren’t dropping fps before.
I can confirm that I reproduced the OP’s problem as soon as a logged on after 9.0.5. This is not an addon issue, I’ve disabled all of them and experienced the same problem.
Edit: Before patch 9.0.5, recommended settings were at graphics slider 5. After the patch, the recommended settings are now 2. Hardware requirements increased with a minor update?
Edit 2: Disabling vertical sync somewhat alleviates the FPS drops. However, with vsync off the game gets stuck to the point in which the only solution is a hard shut down. Happened once last night and once again today, ruined someone’s m+ key 
Hey there,
Thanks for reporting this. To better assist y’all I’d like to collect some information. Please reply with the following if you are a Mac user with an M1 chip.
This information can be found by clicking the Apple menu and selecting About This Mac. Info on this from Apple is here.
Thanks again for the reports!
Hi,
My specs:
Thanks for looking into this!
ty!
Hey, glad to know I’m not alone. Prior to today, I was running on setting 10 and getting 60FPS continually, now I am hovering at 17-20 FPS. Dropping down to even setting 3 or 4 doesn’t do much (I get a few more frames but that’s it).
OS: 11.2.3
Graphics: M1 8-Core GPU
Processor: M1 8-Core
Memory: 16 GB
OS: 11.2.3
Graphics M1 8-Core GPU
Processor: M1 8-Core
Memory: 16GB
Ran like butter in most spots before, now runs like doodoo even with no addons.
Thanks for looking into this - same issue. Choppy frame rate last night, first time I’d logged in since the patch.
OS: 11.2.3
Graphics: M1 8 core
Processor: M1 8 core
Memory: 8GB
I just want to comment that this problem is not only affecting M1 chip machines.
I am running a 2018 MBP with an I7 6-core and the Pro Vega 20 GPU. Since 9.05, my fps has dropped from 40-50 to 15-20 consistently. I have 32gb of memory. Tuning down particle density and texture resolution has helped get it back to 20-30, but it is definitely lower since the patch.
I made a separate post about having FPS issues on non M1 machines but figured I would reiterate here. Also happening on my MBP 2019 i9 16GB machine. Not happening everywhere in game but before patch never dipped below 60, now getting 40’s in some instances. Near impossible to reliably tank higher keys at 40 FPS. Please help,
Ergo
OS: 11.2.3
Graphics: M1 8 core
Processor: M1 8 core
Memory: 8GB