Look up the freestyle arrow technique. They say about 30% of forward speed comes from legs, but those are the big muscles. I’m no expert, but that seems logical.
Fins could help build leg strength specific to swimming? (Freestyle, backstroke, maybe butterfly, but definitely not breaststroke).
Do a few 50s with a kickboard, no matter how much you dislike it. I’m around 50 and I also have a very weak kick, but I’ve started to improve a bit since I’ve been forcing myself to do at least a few 50s of kicking every time I swim.
Try this drill where you kick 5-10 times for every pull. Like, do one arm pull, then extend the other arm in front while kicking 5-10 times (your choice). While still kicking, pull with the arm in front and then switch sides. This drill helps you sync your kick with your pull.
I struggled with kicking my whole swimming career. I never found a trick to do it without thinking; the moment I stopped concentrating on it, I’d stop kicking.
As a former competitive swimmer, I never kicked then, and I still don’t kick now, haha.
Use fins and a kickboard. Kicking should make up at least 30% of your practice routine.
Grab the edge of the pool and practice kicking. Use a kickboard and fins. Kick, kick, kick.