You don’t need the carbs for working out or a pre workout snack.
If you want it, I guess go for it, but it’s not necessary.
Definitely take a good dose of electrolytes prior though and I don’t mean Gatorade. I mean sodium mostly but if you want to make ketoade or snake juice or sole water or whatever thing people are doing now, then do that.
Also, it’s almost a certainty that people gain weight when they start working out. You retain water.
Also, you can lose fat without losing scale weight.

I have been working out since I was a teenager. When I went keto, I did notice a slight drop in performance. Carbs were not the answer. Increased protein is what helped me. From a weight loss standpoint, protein is more satiating which helps control overall food intake. From the muscle building standpoint, nothing is better than protein. Protein is also able to be converted to glucose by your body IF NEEDED.

There are 2 primary reasons for pushing carbs ahead of a work out. The first is for the energy with the thought that you need the glucose to fuel the activity. When looking at this logically, it doesn't make sense - especially if you are trying to lose weight.

You have 2000-2500 calories worth of glucose stored in your muscles and liver in the form of glycogen. Unless you are running a marathon, you are not going to burn through all of that in a single workout. Therefore, you have enough glucose supply to fuel the level of activity you are likely doing.

That activity will deplete some of that glycogen. Over the next few hours, your body will replace it. This will be done, if you are keto, through gluconeogenesis (the creation of glucose from either protein or fat). Assuming you are fat adapted, each time you are burning fat, the glycerol backbone of the triglycerides being burned is one source being used for this process. This is what you want to have happen. Burn the existing glucose stored in your body and replace it with fat pulled from your body. It is like eating what is in your fridge and replacing it with what is stored in the freezer. Keep doing this without replacing what is in the freezer, and eventually that freezer will be empty.

The second reason is because carbs spike insulin and insulin, in addition to helping store fat, helps to stimulate muscle growth. However, protein also raises insulin, although not nearly as much. It does raise it enough to stimulate muscle growth, so there is no reason to spike it further with carbs unless you are looking to become a competitive body builder.

There is also more than enough evidence in the scientific literature (look up Jeff Volek's work as an example) showing exercise in a fasted state is as good or better than in a fed state. I personally have been doing morning work outs in a fasted state for years with above average results. Here is a fairly short video giving some of this evidence if you are interested:

https://www.youtube.com/watch?v=6d0DZklfCEo

People can respond differently, so I always encourage self-experimentation. In this case, it sounds as though you have been doing a self-experiment which is not working, so maybe it is time to change it up.

FWIW, when I taught fitness classes I was usually in a fasted state (unless it was the evening Athlete-Fit). There was never a problem with energy & that was for 25 years of teaching. Water and electrolytes, though - those are necessary!