Hi@Momin8454 @Traceur finally I am in TWRP now! Thanks a lot guys! really appreciate your help.
I am not sure what was the issue, but I did followings (writing down just in case this will be helpful).
PRA-LX1 c646 (I have seen some issues reported for this model, maybe I need to change the build and then try again???). Bootloader unlocked. I was not able to get into TWRP. I was able to get into fastboot. eRecovery from Huawei was not doing anything (cannot get info from server it said).
Then I downloaded the FullOTA-MF (provided by @Traceur but I guess it is from Huawei Firmware Finder.)
dload method was getting interrupted after 5%.
Then I extracted System.img kernel.img, recovery_ramdis.img and ramdiks.img. and flashed these in order.
System – fastboot flash system SYSTEM.IMG
Ramdisk – fastboot flash ramdisk RAMDISK.IMG
Kernel – fastboot flash kernel KERNEL.IMG
Recovery – fastboot flash recovery_ramdisk RECOVERY_RAMDIS.IMG
Then at reboot it was getting stuck at 0% loading (Warning To avoid system error please do not press and hold the power button) on some EMUI page. Waited for half an hour and rebooted. again stuck. went into bootloader and flashed a TWRP. this time I get into TWRP.
so my next step is to get the LineageOS working. trying the same way as suggested: Dil3mm4's TWRP and the LineageOS 17.1 by joker (installinng gapps, magisk and pathces in TWRP as in OP). everything goes fine, no errors. but when I reboot it first does another reboot and then goes into Huawei eRecovery.
Glad you can get in twrp now.
By the way i didn't provide a link. Some other guy did. I just said to use firmware finder
And before you said your phone is c464 and now c646. Which one is it?
I think now that you are on twrp use hurupdater to install a stock rom and then install a custom rom to make sure everything is fine with your phone.
Try doing factory reset with stock recovery or twrp and if it didn't work, use hurupdater.