Named user accounts are used to identify a person who can access UiPath products and services, and can be assigned roles, licenses, and groups. User Robot accounts are used to run unattended processes that do not require human interaction, and can also be assigned permissions and groups1.
References: About accounts and groups

The fields of an entity are used to define the attributes and relationships of the entity, such as the name, type, format, and validation rules of each field. The fields can be of different types, such as text, number, date-time, relationship, auto-number, choice set, and file. The fields can also be customized and modified according to the business needs.

Solution architects are responsible for designing automation solutions and choosing the technology stack for the development and operationalization of the solution. They are also responsible for overseeing the development and implementation stages. One of their key responsibilities is to coach developers on the best practices in an RPA project, such as following the UiPath Automation Implementation Methodology, using the UiPath templates and solution accelerators, applying the principles of modularity, reusability, and maintainability, and ensuring the quality and performance of the automation code. Solution architects should conduct frequent and thorough code reviews to enforce a high standard of the developed workflows and to facilitate knowledge transfer in the project team.
Reference:
Become an Automation Solution Architect | UiPath Academy
Roles of a Solution Architect in Automation, RPA Setting - UiPath
Studio - Automation Lifecycle - UiPath Documentation Portal

UiPath Automation Cloud is a cloud-based enterprise automation solution that lets you start and scale your automation from the cloud with SaaS robots and self-hosted robots. It offers security, compliance, governance, and insights for your RPA initiatives. It does not require manual installation and maintenance, as it is delivered as a service. It does not have single or multi-node deployment options, as it is hosted on UiPath's infrastructure. It does not provide major updates twice yearly, as it is updated continuously with new features and improvements.
Reference:
Complete cloud-based enterprise automation solution | UiPath
Automation Cloud - UiPath Documentation Portal
Automation Cloud - About Automation Cloud - UiPath Documentation Portal