I found this for a 2019 CT5 on YouTube. Hope it helps.

Maybe not, this is for a CTS, but the filter is usually behind the glove box.

 

I am asking the same question for a 2021 CT5. I think it is behind the glove box, as I can see what appears to be a little door than can be opened from the right. However, I cannot figure out how to either remove the glove box or lower the swinging glove box door to get more room. Any ideas?

 

under the right outer cowl panel, like on the CTS ?

 

You have to remove the glove box door. It is (apparently) in behind there.

 

I get that, just cannot figure out how to remove the glove box door. It's not the same process as older CTS.

 

its not in the owners manual? mine is....

 

Sadly, no...manual states it is a dealer item...

However, in the interim I found a YouTube video showing how to do it on a 2020 XT4, which is essentially the same setup as mine. It involves taking the tension damper wire off (easy) and then removing the glove box pins from underneath, thus allowing the glove box to be removed and then access the filter door. Viola!

 

check it out:

 

It is not necessary to take out the pins. The way the box looks in the XT5 is very similar to the video for the XT4, and as a member above stated looks similar to the CT5. In my XTS once the dampener is removed the glove box bumpers are pressed inward to release them, the glove box door then drops straight down. For the XTS there is another item to remove before getting to the cabin filter. In the XT5 once the glove box door is dropped down it reveals the area where the cabin filter is. Take a look at a CF member's video to see how it is done for the XT5. I bet it will be similar for the CT5.

 

This maybe late as I see this is a pretty old post and I'm brand new here. Anyway, I still have not found anything for our generation of car 2020+ CT5, but I may offer a suggestion to look at You Tube under 2016+ Camaro cabin air filter changes. There are probably a half dozen videos by now that show great detail on how to get behind the glove box. My wife has a 2018 SS which is also an Alpha platform car like ours and I strongly suspect that our cars are the exact same way. I have changed hers a couple times already (every 2 years). The only thing you have to be careful of (assuming they are the same) is to pull back and hold with a small string or bungee the retractable wire that is on the side of the box itself. Then with a little bit of force by pushing in the sides of the box, "wa-la" you can now gain access to the filter cover for replacement.

 

I see the video a few posts up this thread of the XT4 maybe the closest thing to how ours are -at least gives you an idea of their location. Also, here is a You Tube that is pretty good for the Camaro (alpha car) that is most likely how the CT5 is as well:

If I had to replace my filter today, this would be the first thing I would try.....

 

I just replaced the CAF on my 2020 CT5 (base 2.0L 4 cylinder). The filter is behind the glove box. Usually, you can find a YouTube video for ANYTHING, but I found nothing for the CAF on a CT5, but in general, most of the Cadillac videos I found mentioned the behind-the-glovebox location as a likely spot for most late model Cadillacs.
It was a little tedious, but not too daunting. After emptying the glovebox, you can drop it down enough to access the CAF location by gently squeezing each side of the glovebox inward to disengage the lugs on each side that limit the opening travel, so you can drop the door down a few extra inches to access the air box that houses the CAF. You may have to do one side at a time. Be patient, it's easy to apply too much pressure to plastic. In the videos I could find, they mention undoing the cable on the right side that dampens the opening speed of the glovebox. But for whatever reason, I couldn't get it undone, so I just left it attached.
Once you've got the glovebox door open as far as it will go, the CAF access panel is visible. It's a rectangular panel about 1.5 inches high and about 9.5 inches wide. On the right side are two "ears" that you have to squeeze together (vertically) to unlock the access panel. It's a snug fit, but unless you have huge hands it's not too daunting. Once its unlocked pull the right side outward,(towards you) and then slide the door to the right to undo the locating tab on the left side to remove the door.
Once the door is off, removing the old filter is very easy. It slides right out, and you can insert the new one by sliding it into the opening. The air flow orientation arrows should go from top to bottom. I went with the Purolator One filter impregnated with carbon for odor control.
Re-install the door in reverse order by inserting the tab on the left side back into the air box, and gently press the right side in until the "ears" lock back into place. On mine, I found I had to get the bottom side started before trying to get the top side set.
Sorry I didn't take any pictures or videos, but by trial and error, I got it done. May have spent 45 -60 minutes tops getting it done. Good luck

 

Sorry I didn't take any pictures or videos, but by trial and error, I got it done. May have spent 45 -60 minutes tops getting it done. Good luck

Thanks for confirming, sounds just like the Camaro video above. Which PN air filter did you use? I see a couple different AC Delco PNs on rock auto.

 

So apparently what I stated is true; it is like the Camaro. Obviously Growler76 did not see my post first? Anyway, the part number is the same as the Camaro ironically enough - AC CF185 which confirms they are indeed the same same thing. It's an Alpha II thing...