Dear member,
Thank you for posting your question on the Microsoft Q&A platform.
Recently I installed the BizTalk2020 Dev edition without any issue, it might be you have to download the files properly.
Could you please provide more information about your system configuration and which edition of BT2020 you are installing?
Kindly share the link from you downloaded it and confirm if you checked the system compatibities.
Regards,
Kamlesh Kumar