Debian have a patch for that.
I've tried Debian's patch and it crashes on the first fb2 file I've tried. Py2 version works, so it's not a complete patch.
The bug has been referenced in the following commit(s):
Author: Michał Górny <email@example.com>
AuthorDate: 2020-09-01 06:06:10 +0000
Commit: Michał Górny <firstname.lastname@example.org>
CommitDate: 2020-09-01 06:06:10 +0000
package.mask: Last rite app-text/fbless
Signed-off-by: Michał Górny <email@example.com>
profiles/package.mask | 7 +++++++
1 file changed, 7 insertions(+)
Package was removed from tree