[Google Pixel 4 XL Accessories] bdt1995:
(TL;DR) In short, they exist, but as a concept, they really just don't work well. Here's a link to one anyway: https://www.amazon.com/dp/B07CXV4RXQ that I mention later on. It appears to be the same, or similar to the one tysj mentioned, so, it may or may not work, it really depends on the positioning of the magnets.

Thing is, like tysj found out the hard way, it's not really something that can be done (effectively, anyway), because as you probably know, Qi charging isn't magic. It's inductive charging. (Keep in mind this is a simplified explanation, it's actually a bit more complicated than this, it uses inductive resonance charging which has a bit more to it allowing it to be more efficient and have a longer range, but at the base it's still an inductive charger, just with a capacitor to set the resonant frequency and range with peak efficiency) Meaning, the charger is running electricity (AC) through its coil, which creates a changing magnetic field, which induces an electric current (AC) in the coil in the device you're charging (it's converted to DC before it charges your battery.)

Essentially, it goes (Wall AC) -> DC (wall-wart/car) -> AC -> coil -> changing magnetic field -> coil -> AC -> DC

So, placing a pair of permanent magnets in the middle of this, right where the changing magnetic field needs to be, only serves to block the ability for the charger to change the magnetic field, which it tries to compensate for by putting more power through its coil. Let's just say that in a fight between the coil and a permanent magnet strong enough to hold up your phone, the coil loses, as it is no where strong enough to change the magnetic field of the magnet. While the charging coil's magnetic field and that of the magnets may, in places, be shaped in such a way to allow some of the chargers coil's magnetic field to reach the device coil if precisely positioned, most wont, and the permanent magnets will just further resist any changing magnetic fields in the device coil.

It could possibly be done with very careful and precise positioning of magnets, like this one from Amazon.com, for instance, although based on reviews (and tysj's reply) I'm unsure of how well it will work, and it certainly depends a LOT on where you put the magnets on your phone/in the case. That's a link with no referral code, and no tracking info, I always strip them when sharing, as a courtesy just the link. Since the location of the coil in the phone isn't standardized, it's hard to say. I'm not an electrical engineer (so there are most likely errors in here), so I honestly couldn't tell you. But as someone who has a (very) basic understanding of electromagnetism, including induction, this is really not a good idea.

In the past, I had a magnet in my phone's case for just that reason, and trying to use the wireless charger just created heat, and didn't really charge the device. And that was without a magnet on the charger, too.

If you want to read up on how inductive charging (including Qi) works, the Wikipedia article is pretty good. Wikipedia: Inductive Charging

I know you said that you

but, given the above, I strongly suggest a Qi mount with an automatic grip for essentially the same functionality, but in a way that actually works. Look around for something quick. I'm unsure if I would recommend the Scosche magnetic one above, just due to how you would need to get the magnet placement nearly perfect. It might be worth a try, if it doesn't work you can always return it.

Something like this one on Amazon.com (there are many different designs like it, this is just an example.) It uses an IR sensor to detect when your phone approaches, then opens, and closes once its on the stand, then it releases by touching a button. It's not quite as easy as a magnetic mount, but at least it'll wirelessly charge.

Either that, or use a magnetic mount and a charging cable.

If you do end up buying a Scosche one, do let us know how it works out.

There's also one that requires a certain case to use, so I imagine there might be more of those. IMHO those are more likely to consistently work, as the magnets are pre-placed in the exact position needed and in a way that wont get in the way of the coils.

Good luck!