@LexYeen split the deck into two roughly equal parts. Then turn upper corners towards each other. Lift from the bottom of those corners with your thumbs and use the rest of your hand to keep the decks down and put the cards under tension. Let your thumbs slide up the corners, which should feather the cards together at the corners. Then tamp them into alignment. Repeat procedure 3-7 times for proper random distribution.
@LexYeen that's okay! That's why you shuffle more than once to help break those clumps up. And as you break in your deck and find the right amount of tension to hold the cards under the clumps should go away.
@LexYeen you can also try getting a deck that has more slippery cards so they don't stick together.
@LexYeen @kelseyhusky Hate to say it, but it just might be a thing that doesn't work for you. My mother has never in her life been capable of shuffling a deck of cards. It was a running gag for a while... then just became a silent fact of life. *hugs* I'm amazed I can manage it at all, not that I've even tried lately.
@LexYeen to bridge after shuffling place your thumbs on the opposite (web of skin between thumb and index finger) with the feathered cards against your palms to help curve the cards back down. Tension should push the feathered cards into a unified deck. This part took a lot of practice. Might want to be prepared to play 52 pickup the first few times. It comes with practice!