Recently I see that BTT needs a lot of memory for something I do not understand
web processes are used for many things in BTT, e.g. rendering previews in the clipboard manager or rendering the notch bar or the stream deck emulator. However usually they don’t use much memory or the system automatically frees the memory when it runs low on memory. (if there is still a lot of memory free on your system, macos might not clear it immediately)
However certain things can lead to high memory usage, e.g. using very large icons for notch bar items.
If memory usage keeps growing it could be a bug in one of the BTT functions
Ok, I recently added these icons, all about 2 cm wide and yes there is still enough memory. I will keep an eye on this. 
That's nice, thank you Andreas. Unfortunately one files is larger than 20 mb, so I can't send it. 
But it is for sure as you say. If the "problem" gets worse I will send you the files from another account.