So if I understand this correctly, the plan should be to flash TWRP BOOT A12 version first via fastboot command after bootloader is unlocked. Seems like the dl.akr-developers.com website is not fully functional (loads slowly for me as well), hopefully it will be sorted in the next few days (as mentioned above I'm still waiting for the BL unlock, so I can wait no problem).Apparently the site no longer works for downloads.
If it is for a first installation, the Twrp you downloaded is the REC not Boot Version.
Wait for the site to work.
[BOOT]3.6.2_12-Mi12_v6.3_A12-cupid-skkk_b62a9844.zip
https://dl.akr-developers.com/?file=skkk/TWRP/A12/v6.3_A12/[BOOT]3.6.2_12-Mi12_v6.3_A12-cupid-skkk_b62a9844.zip
78.63MB
2022-09-13 01:06