I edited my post and added the missing link.I'm very greatfull for your quick reply ! Thanks
The device is too a Poco f3, sorry.. This doesn't need to flash magisk for twrp to stick (I had another one I've broken)
But I don't understand what's the advantage to first flash a fastboot rom..? As you say to flash twrp would loose root and vice versa... (I've read the thread you're talking about ofox)
So I wanted to go trough +- the way I mentionned, as A13 as well as ofox 'seems' to work (but I'm carefull with that twrp on stock MIUI A12, and I never used ofox..)
So you do think it's a bad idea ?? The rom I want to flash is crdroid.
I'm more lost now ...
Thanks again !
If the Cdroid is A13 you will need:
1 / flash the correct Firmware, TWRP A13, (sometimes it does not work, you have to flash the complete ROM) Miflash.
2/Twrp/format data type yes/reboot Twrp
3/ then flash the rom following the instructions of the OP