Reconciliation

React holds the old state as virtual DOM.
When it rerenders it creates a new instance as virtual DOM.
Then it compares

  const [isCompany, setIsCompany] = useState(false);

  return (
    <>
     <Checkbox />
        {isCompany ? (
          <>
            Company tax id
            <input  />
          </>
        ) : (
          <>
            Person tax id
            <input  />
          </>
        )}
      </>

Is companyUse Key

Person tax id

Enter some text in the input. Toggle the checkbox. The input value doesn't reset. Why?
React thinks it's the same component, the same input.

Before re-render, isCompany false, Jsx > js

After re-render, isCompany true, Jsx > js

{
 type: "form",
 props: {
   children: [
     {type: Checkbox, ...},
     { type: "input", ...}
   ]
 }
}

{
 type: "form",
 props: {
   children: [
     {type: Checkbox, ...},
     { type: "input", ...}
   ]
 }
}

React thinks input is the same, so it doesn't remount, it keeps the same element, updates props if needed.
If you want the <input /> to be remounted and state reset, provide a key.
Or change conditional rendering

 {isCompany ? ( <> Company tax id <input  />  </>) : null}
 {isCompany ?  null : (<> Person tax id <input  />  </>)}

This way the children array has 3

 children: [
       {type: Checkbox, ...},
       { type: "input", ...},
       null
     ]