Depending on your situation, as long as you don't very many values in the picklist, you could have separate record types for each value. With separate record types, you can create different page layouts for each one. In many situations, this won't work, but it is a possibility. The nice thing is, you can implement it without any code.
Greetings!
This can be achieved by the visualforce page.Once,you have selected the input then you can write the logic to display the other field.
Please check the related example for the sample code:
https://developer.salesforce.com/forums/?id=906F000000097CzIAI
Kindly let me know if it helps you and close your query by marking it as solved so that it can help others in the future.
Warm Regards,
Shirisha Pathuri
https://help.salesforce.com/articleView?id=000324662&type=1&mode=1
If it helps, please mark as best answer, it may help others
Depending on your situation, as long as you don't very many values in the picklist, you could have separate record types for each value. With separate record types, you can create different page layouts for each one. In many situations, this won't work, but it is a possibility. The nice thing is, you can implement it without any code.