Hi @Winston TheFifth ,
If you using SSMS UI to restore DB1 backup to DB2, please note below key points. If it still failed, please share us the detail error message from SSMS UI by clicking the message beside red X in lower left corner, or get the detail error message from SQL server error log.

If you using T-SQL to complete this job, please refer to below T-SQL; Please change the location of .bak to the correct one in your environment.
1.Determine the logical file names of the database, from the backup file, along with their physical paths by executing the RESTORE FILELISTONLY command:
use DB1
RESTORE FILELISTONLY FROM DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL15.SQL2019\MSSQL\Backup\DB1.bak'

check physical path of DB2
use DB2
SELECT
name 'Logical Name',
physical_name 'File Location'
FROM sys.database_files

2.Restore database.
use master
RESTORE DATABASE DB2 FROM DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL15.SQL2019\MSSQL\Backup\DB1.bak'
WITH REPLACE, RECOVERY,
MOVE N'DB1' TO 'C:\Program Files\Microsoft SQL Server\MSSQL15.SQL2019\MSSQL\DATA\DB2.mdf',
MOVE N'DB1_log' TO 'C:\Program Files\Microsoft SQL Server\MSSQL15.SQL2019\MSSQL\DATA\DB2.ldf';

If it still does not work, please share us the error message for analysis.
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