Preface - I’m no mental health expert. But this is what I would tell a friend if they were in your situation:

You can take the L today and this week. Things in life can feel like mind-numbing pointless exercise sometimes, that is normal. Forcing a smile isn’t going to do anything about how you feel, and turning to vices (overeating, drugs, etc.) compulsively will only create more problems that are difficult to get out of.

Start by coming to terms with your feelings and that it’s a bad day or week. Give yourself time, space and a degree of lenience. You can be your own harshest critic. Write things down, complain to the aether, cry, whatever. Then, let your emotions be what they are and start focusing on what you can control. Even if work isn’t going well, you can prep yourself today or tomorrow’s meal, clean your living space, pick out tomorrow’s outfit, do shopping, check your mail or something else you might have put off. If you’re too tired, then you can work on fixing your sleep schedule. Today there are no bars to clear, no expectations. Get nothing done, or get anything done.

At your next full day off, try seeking out a small change of scenery or pattern. Take a walk through a nearby park that you don’t visit often. Buy a different kind of some grocery item than your usual. Take a bath. Give yourself an opportunity to reflect on your life, what you are thankful for and what you want from your future, however small or big, impossible or possible. Where on your priority list is the approval of your manager? Probably not even on there at all!

I know you will get through this downswing. If your emotion can’t be helped today, then all you can do is prepare for it to be even a tiny bit better tomorrow. Go get it, champ!

Here’s a different framing that might help:

Diabetics are normal people who happen to have a chemical deficiency that requires constant monitoring and chemical intervention. Some days diabetics will struggle to participate in society at all because of sugar level management.

You’re an emotional diabetic, just like me. I’ve got my emotional insulin tuned pretty well but there are still days where I struggle to find the willpower.

Give yourself the space and the grace to have down times, especially since you know during up times you’ll enjoy what you do. See if there’s any self care you can do to make the down times less bad.

Good luck brother/sister.

If you knew someone else was having the same experience as you, would you feel hate for them when they’re not able to get their shit done? If the answer is no then maybe knowing that can help relieve some of the self hate you’re feeling over your circumstances.

I suspect you may even feel inclined to provide empathy and support for the person having the same experiences as you. If that’s true, then you know people having your experience deserve empathy and support. You’re one of the people having those experiences so you’re deserving of the same as others!

@Roflmasterbigpimp well, I am not experienced in helping depressed people, but my naive idea would be, that you might be better if you try to program sth. That could give you a Sense of achievement.
I really enjoined doing advent of code last year, because you have easy but still challenging code puzzles and it has the social aspect of comparing and exchanging ideas with your friends, which is really fun.
If I missed the point of your sadness, maybe just know, that your friends are there for you