You're right, it's available for J7 only, officially there isn't any rom available for j7 max(maybe due to the very low end mediatek chipset and/or lazy developers).
But you can root the device through odin, there are videos available on youtube.
As for netflix and banking apps, it won't work.
Although, you can sideload netflix from apkmirror websites and make it work, it's just that you won't get updates from the play store.
And yeah, you won't get security patches too.
Better buy a new device, low budget if you don't do gaming.
You can use J7 max as secondary and perform experimentation😅
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