https://wccftech.com/2020-mac-mini-update-brings-double-storage-capacity-to-all-variants/

Apple has updated Mac mini with double storage capacity, for both available configurations. For the same price as before, users can now get double the SSD storage capacity than before.

Last year, Apple had reduced the price for storage upgrades for Mac mini, however, it was still shipping the base models with 128GB and 256GB SSD, for $799 and $1,099, respectively. This has changed now as customers can get 256GB and 512GB SSD, for the same prices.