How I can detect my heaviest (cpu and memory intensive) and slow database queries that ever run in my postgresql database?

I thought an idea over a schema & data change over my database. But I want to look whether this change over my database may have a good impact on overall performance on specific queries.

So how I can detect my heaviest queries that use a specific table or views (either materialized or not) that use a specific table?

I also asked in:

https://dba.stackexchange.com/q/278183/118215