This problem is fixed. It seems commit 03a7b67b314286a9185535f5ecbb7cde97ae2c97, or the LyX related commits after this one, fixed the problem.
--- https://sirgazil.bitbucket.io/
bug#41049: LyX: No application icon
sirgazil via Bug reports for GNU Guix Tue, 16 Jun 2020 17:25:17 -0700
- bug#41049: LyX: No application icon sirgazil via Bug reports for GNU Guix
- bug#41049: LyX: No application ... sirgazil via Bug reports for GNU Guix
