SharePoint 2016 is running slowly after the 2013 migration

We recently migrated from SharePont 2013 (standard) to the version of SharePoint 2016 (standard). But, the SharePoint intranet site runs super slow.

The configuration of the new sharepoint environment is shown below:

Application server:

RAM: 32 GB
HD: 800GB
Processor: 4 cores
OS: Windows Server 2012 R2

Database server

RAM: 12 GB
HD: 800GB
Processor: 2 processor
OS: Windows Server 2012 R2

My The size of the content database is 100 GB and the root site that has 20+ subsitesI tried almost everything to improve performance, but I had no luck. I followed the link:
https://www.networkworld.com/article/2210265/tech-primers/10-steps-to-optimize-sharepoint-performance.html

Can anyone suggest, do I need to make changes to the infrastructure or something else?

Help appreciated.
Thank you