Forbes claimed that Rubik's have sold 450 million 3x3x3 cubes since it was released in 1980, and this is just the old Rubik's brands alone, with the rise of interest in speedcubing, it is likely that hundreds of millions more have speedcubes have sold in recent years. Large US cube stores are regularly receiving nearly 500 orders per day, many of which may include multiple cubes. It is very difficult to give any sort of definitive estimate of the total number of cubes sold around the world as we cannot know. MoYu have likely sold millions of Meilong 3x3x3s and RS3M 2020s, and other brands such as QiYI, YuXin, Gan, ShengShou and DianSheng have probably achieved similar targets, while the more real knockoffs from the 1980s probably added many millions more to the total number. I would estimate that the total number of 3x3x3s cubes ever produced will probably be over 1 billion, and that is just for 3x3x3s.
While other products are less popular, they still have received significant interest from speedcubers over many years, 2x2x2s are also popular and sales probably amount to around 100 million, pyraminx is probably only slightly less than 2x2x2, maybe 70 million, we also have bigger cubes such as 4x4x4, maybe 50 million 4x4x4s have been sold around the world and then vastly descending numbers as they go up, I suspect MoYu will have sold hundreds of MoYu 21x21x21s though. Even more obscure puzzles have probably still sold in the hundreds of thousands, even the millions, J Perm's 'Attempting to Solve a PUPPET CUBE (With NO Help)' video has received 3900000 views, while many people will not be interested in actually purchasing the puppet cube, MoYu have still probably sold over a million of them in total. The great thing about speedcubing is that there are so many puzzles to try and the 3x3x3 cubes global recognition means that people are still impressed by speedcubers to this day. These puzzles seem initially to be very hard but people can easily learn how to solve them through a bit of patience following the instructions, and once you can solve them, they are very addictive, how fast can you solve it? Or why not try another one?