So I guess I should clarify that I am not an expert on anamorphic lenses and filters. Just that I do know there are some filters out there that create SOME of the effects of anamorphic.
There are filters out there for adding the flares (usually EITHER blue, or orange, or a neutral color flare), then there are filters out there for the oval bokeh. Not sure if there are filters that can reduce the shallow depth of field in the edges of the frame, but there are definitely filters out there that will reduce the SHARPNESS towards the edges of the frame.
I watched through the video by Rhett Shull covering the BTS of the music video, He mentioned using plugins like Film Convert to give the video a film-like appearance as well.
So, again, I am not an anamorphic expert. Maybe if you poke around on the youtbe channel Anamorphic On A Budget you could get some ideas?
https://www.youtube.com/@AnamorphicChannel/videos
If it were me, I would just think a bit more on what effect(s) exactly you would like to emulate, and then see if you could do it with some (relatively) inexpensive filters and / or free software. I would try to use the 15mm lens on the G9 that you already have.
However, if the 15mm lens is too sharp, you might try looking for an old all manual film lens that can be adapted cheaply, or a diffusion filter such as a black pro mist or glimmer glass or some other type of diffusion filter.
Hopefully someone can chime in with advice on specific filters for you.