The most fulfilling area I've ever worked was with wind turbines. Making software for things that actually mattered, as opposed to dumbass ad tech for ad tech's sake, was very enriching for me.

With respect to algorithms - nobody starts out good with them (except Knuth), it takes practice. Don't give up. Also recognize Leetcode for what it is - practice. It's okay to do a problem poorly/not figure something out. It doesn't actually determine anything about your intelligence or trajectory in the field.