Clean microfibre cloth. The same as used for cleaning prescription glasses. If you want to buy something special then any optician or camera shop would be able to sell you a good lens cleaning cloth.
You only need specialist cleaning solutions when removing microscopic dust is vital, such as when cleaning the sensor on a dSLR camera. A microscopic grain of dust can obscure 1 or 2 pixels which is noticeable. But if this is on the front of the camera lens it would be so small and out of focus that it would be undetectable, even with detailed image analysis. As soon as you fly you'd start collecting new microscopic dust making such thorough cleaning pointless.
To put it in perspective: how do you clean the lens on your phone camera?
Phones regularly get held by sticky/sweaty/dirty hands, put in dusty pockets, placed on dirty tables/desks etc, whereas your drone camera very rarely gets touched by anything other than fairly clean air, so the requirement for cleaning your drone camera should be significantly less than a phone camera, unless you're into touching the camera lens, flying low over breaking ocean waves, through clouds of mosquitoes and landing directly onto dusty ground.
A single wipe with a clean shirt sleeve does the job for me 99% of the time for my phone.
I lightly blow off any visible dirt and then breath deeply to fog up the surface of the lens and then wipe with a microfiber cloth. It’s been good enough for DSLR lenses costing way more than the Mini.......
Just bite the bullet and buy a lens cleaning kit from Amazon around $10. It has everything yo need to clean your camera lens. There are YouTube videos demonstrating the use of Lens Cleaning Kits on drones and cameras. I know it won't take long for the nay sayers and guys who just like to argue any point to start posting, so bring it on.
I have a proper lens and sensor cleaning kit with the air puffer, cloth, wipes, swabs, cleaning fluid, the lot. Have never needed to use it on my drone, but have definitely needed to use it on my dSLR sensor, and a couple of times on an abused lens.
Personally I feel fancy cleaning solutions and the like overkill for keeping a drone camera lens clean. However, don't let my personal view stop you from doing whatever you think is needed to keep it clean, be that a quick wipe with a sleeve, an air puffer, some expensive cleaning fluid and lint free swabs, or the back of a hand . That's part of the fun of this hobby - different ideas and ways of doing things with none necessarily more "right" or "wrong" than the other.