I cannot transfer files from my macbook pro to a pendrive

Most pen drives ship form the factory as Windows New Technology File System (NTFS) formatted. Microsoft has announced they consider that format their proprietary property, and has said they will sue anyone who writes files to such drives without a license. MacOS thinks that is nonsense, and does not participate.

Select that pen-drive in Disk Utility and ERASE to a Mac format like HSF+ Extended or APFS, or to a commodity format like Ex-FAT.

if you select the drive in Finder, and choose GetInfo off the File menu. it will tell you a lot of stuff about the drive, like this:

you can use the drive in my example is a MacOS Extended (Journaled) format drive..

If your pen-drive is [Windows] NTFS drive, it needs to be erased, which can be used to change it to a Mac or generic format that is not proprietary.

What exactly do you mean by "transfer"? Copying the file using Finder from the source to the target is all that's required. Click, hold, drag and drop.

What error messages, if any, do you get?