Okay, so I can confirm that they finally fixed the previous game-breaking glitch. I loaded up a save where I had run into it, and now you can progress past that point to finish the game.
So with Blackest Friday difficulty, much like the main story mode, everything hits harder and you don't get as much health from healing items (now eating people). On top of that, there's a time limit that does not reset whenever you die (though before you die you can pause the game, quit out and come back in to go to a checkpoint.).
However, Frank's zombie powers make surviving pretty simple. Pounce disarms human enemies, including the ones wearing power armor. His spit power does quite a bit of damage even when not fully charged to human boss enemies and acts as a mine when fully charges, and howl is just broken in how you can stun a bunch of enemies at once and get your combo really high. Only issue with the powers is that they're upgraded through collecting items strewn across the maps, completing trials, and completing the challenges in the mode, which the game calls collecting Princess wasps. For the best ending, you need to collect all the princess wasps.
The collectables only show up on the map once you've collected a scanner, but the scanners are already on the map. Just make sure you collect everything before leaving the mall, as you won't be able to get back in. Remember to check on second floors. The collectables you gather carry over to another playthrough, so you keep the upgrades.
The trials are also pretty simple. Run around, eat zombies, collect stuff. For evo zombies you can also eat them, you just need to stun them or hit them beforehand. There are plenty of evo zombies to eat around and in the school, so don't worry too much about it. The trials you complete also carry between playthroughs, so you can always try again if you run out of time.
The princess wasp challenges are fairly straight-forward. There are 'run around and collect these wasp clouds', 'get your combo up', 'survive for a certain time while your health depletes', 'blow up these wasp things', and 'kill these survivors/military folks'. However, they DO NOT carry over to another playthrough. If you start a new game on another difficulty, you will have to do the Princess wasp challenges again!
Run around and collect these wasp clouds: Just keep running. All of them should be simple and in view. For the last one in West Ridge, there are a few outside the house and over the fence, but that's it.
Get your combo up: Now with the zombie's increased health drain this could be deadly, however Zombie Frank's dash now hurts zombies, so for the first one you can just dash around the crowd without getting hurt and get your combo up. Once you unlock Howl, use it, then spam dash until you can use Howl again.
Survive while your health depletes: For this, you'll want to follow the same strategy as above for the combo: Use dash, then once you get your combo high enough, chow down on the nearest zombie. In West Ridge the challenge also adds some soldiers with RPGs, try to find an area where they can't hit you before eating the zombies.
Blow up these wasp things: Run, and use fully-charged spit. The soldiers are annoying, but you do not need to engage them to finish these tasks. Just try to sprint to the wasp thing, charge spit, shoot, onto the next.
Kill these survivors/military folks: These are probably the hardest challenges in this mode, purely because of how much damage guns and explosives do on Black Friday. Even so, they're not that bad. Make use of pounce to disarm people, then beat them into the ground/eat them. For the military folks, their boss is going to run away to summon more goons to hit you, but in both challenges you can pounce him before he gets too far. Make use of howl and the spit move once you get them too, the stuns/damage output makes quick work of these chumps.
Now I will warn you, you'll want get the fully-upgraded melee attacks or the spit move before attempting the military guys, as they have very high health and can stun you, which is basically a second death sentence on BF difficulty.
The last 'Kill survivors' challenge is probably the hardest one, as you have to run though a safe house with six hostile survivors and at the end are two bosses wielding combo weapons you have to kill in a short amount of time. For the bosses use howl to stun them and pounce to disarm them, then spam short bursts of spit to kill them. Even with that it's very tight, I only had about 20 seconds to spare when I finished it.
Now then, none of the main story missions are as bad as the princess wasp challenges. The missions are generally 'Go here and grab this thing', so you can just run in, grab it, and run out. As you're generally surrounded by zombies, you can always grab one to regenerate health while doing missions. The hardest ones in the game are going to the farm and going to the winery, as they don't have much zombies around but plenty of humans with guns. However, at those points in the game you should have unlocked or be close to unlocking all of Frank's zombie powers. Use howl to stun the enemies and get your combo up for quick eating, and use pounce to disarm them and spit to quickly kill them.
The last mission in the lab can be hard, but you can make it one hell of a lot easier just by going around and using spit to set off all the explosives in the area. They're deadly to you on BF difficulty, but in the beginning the lab is empty, so you can just dispose of them then. From there on, it's just waiting for Blackborne to get it together while you howl and eat zombies.
Edit: Forgot the 'blow up the wasp things' challenges.