If you assume Apple continues to follow the 12-month refresh cycle for desktops and portables (as they have been), we'll likely see a new set of Mac Minis and Macbook Pros by EOY (last update was to M1 on 10 Nov and 17 Nov, 2020). Even with the pandemic in play, Apple seems to have gotten a good grasp on their supply chain, but as others have noted in other threads, the loss of many CPU engineers and comparisons yesterday to competitors - versus comparisons to last year's iPhones - may mean incremental refreshes this year.
iMac, probably April since that's when we saw the last refresh (M1). Likely the same for the rumored larger or "pro" model. The Mac Pro has been all over the place and isn't consistently updated, so who the heck knows about that.
