You seem like you should stick to reddit.

KDE has it built in to default key binding of Ctrl + Meta + Esc helpful when in Wayland as xkill only works on X and xwayland apps.

This might help.

https://www.tecmint.com/clear-ram-memory-cache-buffer-and-swap-space-on-linux/

You could write a simple bash script to get memory and compare it to your desired memory usage then clear memory when desired usage has been exceeded. Then set your script as a cronjob.

Or you can just setup a cronjob to clear memory at a set interval in a cronjob described in the link.

Fried duck is delicious!