TL,DR: powder laundry detergent is better than the liquid one.
When it comes to choosing laundry detergent, I used to default to liquid detergent because powder would often clump together. However, I recently learned that liquid detergent has a bigger environmental impact - it contains microplastic particles that are hard to remove in wastewater treatment plants, and it's also less efficient at cleaning. Plus, liquid detergent usually comes in plastic bottles, whereas powder detergent is often packaged in plastic film or even cardboard.
So, I switched back to powder detergent. To avoid clumping issues in my humid laundry room, I found a simple solution: I use an old fork to break up the powder before use. It's a small effort, and I'm happy to be reducing my pollution footprint a bit. Video source (in German, maybe this weekend I'll look for better sources and add an infografic): https://youtu.be/HgIe4oxe2eI
I've used powdered laundry detergent exclusively for almost a decade. We definitely had the dissolving problem at first. We'd get undissolved soap on our clothes.
Our solution was to leave a bare spot with no clothes on the drum when loading, then put the powder in a little pile right there on the bottom. Then start the washer on full hot, and let it fill for 20 or 30 seconds, rinsing the powder down into the lower drum with hot water. Then flip the water temp back over to cool and walk away. The soap dissolves nicely that way. No more issues
Also we were using too much at first, it really doesn't take a whole quarter cup of powder per load like the box says. We get away with a tablespoon or two, depending on soil level.
Hope that helps!