Explanation
Guided selling, validation rules, and required fields on the page layout are three options that can be used to ensure sales reps fill out key fields when working on an opportunity through the process. Guided selling allows administrators to add prompts and guidance at each stage of the path to help reps move forward with confidence. Validation rules allow administrators to enforce data quality and business logic by preventing reps from saving records that do not meet certain criteria. Required fields on the page layout allow administrators to make certain fields mandatory for reps to enter before saving records. Configuring opportunity path can help reps visualize and update key fields at each stage, but it does not make them required or prevent them from moving forward without entering them. Using flow to mark fields required is not possible because flows cannot modify page layouts or field properties. References:
https://help.salesforce.com/s/articleView?id=sf.path_guided_selling.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.validation_rules.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.fields_defining_field_properties.htm&type=5