It's possible to dual-boot. My favorite method is to have a device with a SD-card slot and have android on the eMMC but PostmarketOS on the SD-card.
Currently only do that on one of my older devices, would love to do it on my main device but when I bought it I was in a hurry to get it going and did not have time to unlock the bootloader. Unlocking the bootloader now means having to factory default the device but I simply have too much important stuff set up that it's not worth it. Apparently there's also no great way to backup all partitions of the Android device which I find to be quite strange.
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It's possible to dual-boot. My favorite method is to have a device with a SD-card slot and have android on the eMMC but PostmarketOS on the SD-card.
Currently only do that on one of my older devices, would love to do it on my main device but when I bought it I was in a hurry to get it going and did not have time to unlock the bootloader. Unlocking the bootloader now means having to factory default the device but I simply have too much important stuff set up that it's not worth it. Apparently there's also no great way to backup all partitions of the Android device which I find to be quite strange.