IIRC even though modern hardware Sailfish OS runs on, such as Xperia X/XA2 is internally 64-bit, all the sailfish OS binaries are still 32 bit and the whole system is running in 32-bit mode.
This is likely due to not having to ship two sets of ARM binaries (one for the 32-bit ARMv7 and one for the 64-bit native aarch64).
I'm not exactly sure how this works on the XA2 plus, which has 6 GB of RAM. It could be that the kernel is compiled for 64-bit mode and runs in native 64-bit mode, while individual processes run in 32-bit mode (this is possible and done regularly for modern Linux distros - If you have ever run Steam on Linux, which is 32-bit, you have done just that). That way each process can allocate only up to ~4GB of RAM for itself, but as there are usually many processes active at any one time, the 6 GB of RAM can all be adequately used.
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