(NB: There's no point placing too much weight on what the chip will be called - ultimately, the M2 is whatever chip Apple decides to stick an "M2" label on, or they might still decide to create a separate "branding" for the "Apple Silicon Pro" chips. However, taking the usual understanding that "M1X" is the "pro" version of the M1, whereas "M2" is the next generation of core designs...)
Last I looked, the M2 is expected to debut in the all-new MacBook Air sometime next year whereas the M1X was expected to debut in the 14/16" MacBook imminently (...and may have been held up by component shortages).
When it does arrive, the M2 in the 2022 MacBook Air will, like the M1, be configured primarily for ultrabooks and tablets in terms of number of cores, balance of performance/economy cores/GPU cores, clock speeds etc. and may well have similar limitations on RAM and display support to the M1 - which is perfectly sensible for the target market of 'general computing'. It's likely to be all-round incrementally faster and more power-efficient than the base M1 - maybe 15%.
The M1X, on the other hand, is going to be the M1 souped up for higher-end applications (which in Apple terms usually means graphics, video and audio production). Exactly how depends on which rumours you read* - but a significantly souped up GPU (probably too power hungry for Air/iPad use) is most likely, also supporting more displays, maybe with double the number of cores, probably at least 12 CPU cores, maybe with a higher performance:economy core ratio etc... They'll also have support more than 2 LPDDR4 chips worth of RAM to be credible. For the applications in question - which typically support multi-threading and GPU-accelerated computing - the benefits of the "X" could be far more significant than the relatively small across-the board improvement of M2 over M1.
So, really the 14/16" MBP, 5k+ iMac and high-end Mac Mini couldn't just wait for the M2 say, early next year, they'd need some sort of "M2X" which is probably a lot further down the pipeline.
(* Of course, Apple are not infallible, and the M1X could turn out to be a pathetic warmed-over version of the M1 that doesn't meet the needs of higher-end users, but we can burn that bridge when we come to it...)