Table optimization in Postgres

I would like to understand, why is my database (postgres in docker) that slow.Table has 35 columns and 3.8m records. Table size is rouglhy 2GB.

The queries which I typicaly do here is:

SELECT x, y, z       count(distinct(w)) AS count_1FROM criminal_acts where y like 'xyz'GROUP BY 1, 2, 3;

Normaly this kind of query tooks like 12-15 secunds, which from my point of very slow.About indexes is user can choise x,y,z parameters and also for where condition user also chose whatever he want to filter out in our application.

I am wondering which measures should I take to improve performance ?

I try with vacum and adding every column to index but improvement is very minior.Is probably problem with docker or virtual machine we had 8gb of RAM, and disk has following stats:

sync; dd if=/dev/zero of=tempfile bs=1M count=1024; sync1024+0 records in1024+0 records out1073741824 bytes (1.1 GB, 1.0 GiB) copied, 1.505 s, 713 MB/ssudo dd if=tempfile of=/dev/null bs=1M count=10241024+0 records in1024+0 records out1073741824 bytes (1.1 GB, 1.0 GiB) copied, 0.244821 s, 4.4 GB/s