using [array get bela_multiplexer]
seems to be much better. The below ,which is for illustration purposes only as it doesn't have the same numbers as yours, runs at about 26% CPU.
PS:
Totly he file is only a few kb and still hangs on chrome and firefox, mac and win (edge).
on Mac/Chrome I cannot even select non-image files from the popup dialog when trying to attach a file: