Hey everyone thank for you company

[Wyorp Rock]

The only way to know exactly what this is that is afflicting your rooster is to take him to a vet and have cultures done on the exudate from his vent. If that is not an option, then we can make some educated guesses. My guess is along the lines of what @Eggcessive has mentioned. I think he may have a combination of bacterial and fungal infections that are well established and may no longer be responsive to treatment. However, I always attempt to treat as you never know if a chicken has a strong will to survive.

If you want to try to treat this rooster, it will require daily soaks in Epsom salts and a disinfectant such as Betadine which will act on both fungus and bacteria. And he should be given an antibiotic such as amoxicillin and an anti-fungal such as metronidazole together. You can order them here. https://www.valleyvet.com/ct_detail.html?pgguid=30E072F2-7B6A-11D5-A192-00B0D0204AE5 and https://www.valleyvet.com/ct_detail.html?pgguid=E68FC9E3-30C2-402A-88C4-567BDED2C139 Give one of each daily. for at least one week and see if he improves. If there is improvement, continue for another week.

Thank you for the newest picture. I can’t say for sure what this is, but the yellow stuff looks like cheesy pus. He may have been pecked or constipated and had an abscess form on his vent. Hard for me to say. I haven’t seen that before. If he has vent gleet, he might get some benefit from a warm Epsom salts soak to his butt daily,,followed by applying some vaseline or Monistat 7 cream. Monistat cream can also be given orally twice a day 1/2 inch. If he is constipated chilled coconut oil cannbe cut into small pieces and fed to him to soften his poops. Plain unsweetened yogurt or probiotics can be given in his food. @azygous has seen a lot, and I will also tag @dawg53 and @Wyorp Rock and hopefully others will have a look.Welcome to BYC.

I agree, soaking and treating as suggested would be what I'd try if vet care is not an option.
I'd also be inclined to deworm and treat for Coccidiosis as well.

Work on hydration, offer wet poultry feed (chick starter or all flock feed would be best), provide grit free choice.

A photo of the front/profile of him would be nice so we can see what he looks like as a whole.