After you install the Fastboot ROM, nobody prevents you from installing a custom recovery. However, for MIUI 13, A12 you have to carefully choose the TWRP or OF for your model that properly supports decryption - but there are many posts here about, a thread specially for custom recoveries, another with best practices how to install them and so on, SEARCH is your friend
Things like that were extensively asked and answered here. When reading, do not concentrate only to posts specific for your device, since there are general questions and answers that in one or another way might be useful for the other models (like a link to where to look for the custom recoveries for A12, how to install them, etc)