Customizing list forms inside modern experience, by adding cusotm JavaScripts + custom CSS

I am working on a sharepoint online site collection, and i have 2 custom lists (Depts + Employees), where i want to do these modifications to their lists' forms:-

1. inside the Dept display form to add a hyper link, which reference the create form of the Employees list + pass the current Dept display form url inside the "Source=" parameter. so users can add employees under the current Dept, and when they finished adding the employee item, they will be redirected back to Dept display form.

2. hide certain fields inside the Edit forms, based on the selected item status. for example setting the item status to be "closed", will disable all the fields inside the display form, etc..

now i can achieve the above points inside classic interfaces by modifying the relate list forms and then adding some JavaScript code + CSS.

but if i render the 2 lists in modern experience , seems i do not have the ability to modify these forms. so my question is, if this is currently a limitation inside sharepoint modern experience? or there are ways of customizing the lists' forms in modern experience to allow me to do the above 2 customization ?

Thanks in advance for any help.