Speculation is that Tesla will eventually and officially provide such a solution. In fact, it's already possible
unofficially, and the official solution for a 2021 Model 3 is likely to be similar or identical to the unofficial solution available today. See
this very long thread for information on this unofficial solution. In brief, for a 2021, you'll have to replace the charge port ECU, which Tesla sells for $140, the caveat being that many service centers are reluctant to sell the part.
Much of the thread I've cited covers the more complex task of doing the upgrade on older cars, which require some extra fiddling, in the form of an adapter cable so that the older ("Gen3") charge port design works correctly with the new ("Gen4") ECU. For a 2021 without CCS support, though, your car almost certainly has a stripped-down Gen4 ECU, so swapping that out with a non-lobotomized Gen4 ECU and doing a software re-install is all that should be required -- except of course for obtaining a CCS1 adapter.
The first post in that thread has been kept up-to-date, so you can read that and perhaps the last couple pages of the thread to get a good idea of what the upgrade entails. The thread has been closed because it was drifting too far into discussions of how to buy the "bundle of wires" and other things that were being sold by thread participants.
Of course, if you don't want to do this upgrade yourself, you can wait until Tesla releases something official. I have no idea how long you'll have to wait, though.