Hello, @rwzi

Hope you are doing well,

Yes, you can define group for the specific user using following ways:
 
1. You can define a groups for different users and create a category for the groups
- Please refer to this link for how to define groups:
https://www.odoo.com/documentation/16.0/developer/reference/backend/security.html? highlight=group#res.groups.category_id 
 
2. After creating groups you will see in users there you can assign the different groups created based on group selection, you can group user accordingly to website
 
3. You need use these groups for your website page for user to access or view

I hope this will help you.

Thanks & Regards,
Email: odoo@aktivsoftware.com
Skype: kalpeshmaheshwari