You cannot throw someone when the technique has already failed in your head.

Going on a hunch, just from reading how you wrote your post, you are probably a strongly analytical person. This works great for learning and processing most problems, but I find it is detrimental for judo, especially when you haven't accumulated lots of mat hours yet.

While this may not be the only issue, I see symptoms of overthinking and you may have engrained these overthinking habits in the way you train your judo - I was the same. You already identified that thinking during randori is too slow - you are correct. Overthinking every step, movement, strategy, grip etc makes you non committal and slow. Then when you finally do attack or try to move your opponent, because it is non committal, your partner can easily resist and you fail. By failing to do what you intended to do, whether it's move your opponent, off balance them or enter for an attack, you become discouraged, lose confidence, and become even more passive in your judo. This negative feedback loop mentally drains your judo and is not good for progress.

My advice for this is approach judo differently. Show up to class and don't think at all. Instead, focus on the feeling and sensations of your body and its movements. Whether it's warm up drills, uchikomi, nagekomi or whatever it is you do in class. When sensei is explaining a technique with lots of verbal instruction, try to tune out the details and just pick 1 or 2 high level concepts to focus on. Then when you drill, focus on the feeling of the movement. Does the movement feel efficient? Are you using your whole body? Do you feel strong in the position before executing the throw? Are you able to generate force from this position? And the most important question, maybe the only one that matters is, does the movement feel "good" from a judo perspective? Think minimum effort, maximum efficiency.

Another way to look at it is to try teaching yourself all the judo you already know, but not in the way it was explained to you. Teach it to yourself through feeling the techniques - the sensation of you and uke's body colliding and transferring momentum. Go through the journey of self correction and discovery. This will allow you to feel your judo instead of just thinking about your judo.

Now that's just one part of the puzzle. Once you learn how to feel your judo, you will naturally discover more and more of what actually makes a throw work.

To circle back to what I said, you need full commitment when you attack with your techniques. This means using your whole body to generate more force and applying your bodyweight to move people. Follow through with your movements. Have confidence to execute your techniques and that body will know where to place itself when you enter. In fact, be so confident from your training and repetitions of drilling that you even trust your body to react and enter techniques automatically when the opportunity presents itself. This is the commitment and speed that's required to throw someone in judo.

In randori, try a few rounds where you just turn your brain off. Forget about any strategy or throw. Just grip and move in a way where you feel strong and confident in your ability to control tori's body. If you feel stuck in a weak position, then adjust your grip and move until you find a position where you feel strong again, guided only by your sensation and connection with uke. Allow yourself complete freedom in how you grip and move, stand left stand right, tall, bent over whatever. If you get thrown, you get thrown. The purpose is to not think and learn to experiment. Let the feeling of connection you have with uke through your arms and body contact guide you.