Need to know about Plugin(Add on and Add off Feature) in Saas Application

Need to know about Plugin(Add on and Add off Feature) in Saas Application

Hi Team, I hope you are all doing good. I have some concern and need some ideas about Plugin Concept to involve in Saas application. I hope Zoho Hrms product are based on Saas. I like to ask some question regarding this matter.
1. Based on Client Requirement, we want to add-on and add-off some features in certain module.
2. What are the best approach to go on Plugin concept in Saas?
3. Apart from traditional way like flag setup in database(Tenant based approach to keep their Access data in Table) like Hide and Show. Is there any other better way to achieve this?