Batch add cover art to 800 albums

Firstly, it's great to see MP3Tag still going! I have not tagged MP3 files for about 10 years, and must have had MP3Tag years before that... but it looked very different.

I have just copied all my Flac files to MP3 and many do not have cover art in the ID3 or in the album folder.

Is there a way to globally add cover.jpg to the folder and also to each file, but to have MP3TAG do it in a batch rather than one album at a time? If so, I would love to know how.

Thanks, cheers,

No, MP3tag can do it album by album.
If you need other functions, try the albumartdownloader.
If you have the flac files already with embedded covers, you can copy the tag data including the covers from the flac files to the mp3 files. This works even for more than just one at a time if the flac files (source) and the target files (mp3) are in the same order.