I need to define the strategy and roadmap for Enterprise Architecture from scratch. Considering the company has the lowest level of maturity, what do you suggest in this scenario?

I agree with Manuel Rivera Aguirre

Start with; "what is the EA function for?" - such as.
- Provide EA consulting to help inform, guide and coordinate digital decision making.
- Tailor tools, platforms and guidance to stakeholders of differing abilities.
- Align architects with product lines to provide support closer to the point of decision making.

Why
- Understanding of Enterprise Systems with Ability to plan and develop integration strategies for the Business needs (not technology wants)
- Holistic Mind-Set with the ability to align business strategy with IT strategy and Understanding of the relationship between business strategy, technology and operations
- Cross-Enterprise Perspective, ability to identify opportunities for efficiency and reuse

Create a chapter, mission and vision statements with short and long term goals

Mission statement could be; The mission of the EA programme is to facilitate informed, coordinated planning, guide project delivery to improve consistency, business enablement and control risks to an accepted level

Short term goals; 
Create architectural lite-weight governance guide teams.
Establish EA services for stakeholders, such as business leaders and delivery teams.
Dev architecture resources to provide guidance, identify synergies
Establish coordination to guide charge planning

Long term goals; 
Establish reference architectures
Create pattern libraries
Robust set of architectural guardrails
Shape digital business strategies
Create capabilities taxonomy/framework that enables the business - later map technologies that enable those 

Create and CMMI maturity plan

        Stating your main goals for Enterprise Architecture (such as improving agility, reducing costs, or supporting digital transformation) will help ensure that suggestions are tailored to your needs.
        Instead of only mentioning the low maturity level, you could add: "Our main objective is to enable faster decision-making and support upcoming cloud migration initiatives. What steps should I prioritize in this scenario?"
        
        Including information about resources, timelines, or organizational challenges will allow for more practical and actionable recommendations.