Steve made a pseudo-stereo plugin for Audacity which is available here … Pseudo-stereo effect
Frequency analyses do show the frequency content on each of the “stereo” tracks is a little different …
[and I suspect in part this frequency content difference is not constant: it will change continuously due to variations tape tension / tape position on the player head]
I hadn’t visually noticed the ~10 sample (~1/4000th of a second ) phase shift Steve mentioned,
that delay would contribute to a pseudo-stereo effect, along with the different frequency content.
Note: you could create a mono version by just discarding one of the “stereo” tracks: split stereo to mono then delete one track.