
Hi @Volesini Matej,
What environment is your idea based on, SharePoint Online or SharePoint Server? As per my knowledge, there is no OOTB way to achieve this in SharePoint Online. Found an alternative method by integrating with Power Apps, please see this post: SharePoint form cannot display additional field form lookup column. You can get help from Power Apps experts via posting here if you need further help: Microsoft Power Apps Community.
If you are working in SharePoint Server classic list, you can achieve this via injecting JS to the New Item form. See this demo:
SharePoint list custom edit form show related lookup column field values.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.