The little green arrow (aka playhead/recordhead) is not visible during playback / recording in 2.3.3 (cf. https://bugs.launchpad.net/ubuntu/+source/audacity/+bug/1877833). Installation is from standard Ubuntu repo.
This bug can be reproduced on FC 32 running Plasma 5.18.5.
My initial assumption that this is a GTK3 packaging issue doesn’t seem to be valid as this bug is reproducible across distros and Audacity versions. It also manifests itself in custom builds of 2.3.3 and 2.4.1 on Ubuntu using GTK3.
More than happy to provide more information - just let me know.