Apple has now, as of this week stopped selling the old Intel 21.5 iMac on its online store. The base model has been left on sale since Apple introduced the brand new iMac 24-inch back in April, with the Apple M1 SoC and new colours.
This change affects the Apple online store and its retail locations, third party stores will still stock it, so long as stock lasts. The model that has been dropped had a 2.3GHz dual-core 7th-generation Intel Core i5 processor, 8GB of RAM, 256GB SSD, and Intel Iris Plus Graphics 640.
The only iMac options now are the new M1 iMac and the existing 27-inch iMac, which is due to be refreshed soon with Apple Silicon.