Problematic read queries

Hi Team,

We have recently configured replica to our postgres instance.
Now the application team wants to move problematic read queries to read
replica.
We have enabled pg_stat_statements extension.

1. How can I get most load causing queries from pg_stat_statements view
whether we can calculate it from column 'rows' or 'shared_blk_hit' or
'max_time' or we have to look into any specific columns for that particular
query?
2. I just want only read queries which should move to read replica: I could
see a few select queries calling functions, but functions have
insert,update statements so in that case whether it will be only select
query or insert,update query?

Thanks in advance.

Regards,
DBA