Root problem

[Shogunotaku]

I have rooted my phone long ago and installed the lingae os and now I want to install the pixel experience os on it and my PC isn't detecting my phone when I connect it in flashboot mode to access twrp is there any other way I can get to twrp and supersu says my phone isn't rooted but I did root it or eles I can't be running lineage os ,plz help.(phone=redmi note 4 mido(SD)),

 

[Rukbat]

You root the firmware, not the physical phone, so if you installed a new OS, unless it's rooted, "your phone" is no longer rooted. (And lineage doesn't come rooted. Look on their site for rooting instructions.)