BIAB does support triplets in an even style but it is often difficult to get it to print / show correctly. It will always play the triplet, but the visual may not be right.

One of the notation options is to allow triplet resolution. If you are working in an even style, this option is OFF by default; it is ON for swing (triplet) styles.

You can change it at any point, and then change it back as needed. So enter your notes as required, up to the point you want a triplet; switch the notation option to triplet resolution, and add your triplets, and then switch it back. The playback will be correct, but the print out or screen may look strange.

The is also a way to change an individual note by changing the BEAT resolution. Check it out in the help screen.

BIAB for Windows Version 2019 (643)
Windows 10 (1909)