You can set customize the location as per your need,
Create a file named config_local.py (if not already present) at your installation location ../pgadmin4/web/
and add below 3 lines in it,
import os
DATA_DIR = os.path.realpath(os.path.expanduser(u'~/.pgadmin/'))
LOG_FILE = os.path.join(DATA_DIR, 'pgadmin4.log')
restart pgAdmin4 and check if that solves your problem.