On a fresh copy of the sxmo 1.3.0 image, following the "Upgrading" instructions in the User Guide produces a dependency error.

~ $ sudo apk update
fetch http://postmarketos1.brixit.nl/postmarketos/master/aarch64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/edge/main/aarch64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/edge/community/aarch64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/edge/testing/aarch64/APKINDEX.tar.gz
2021-03-17 20:45:56.611777 [http://postmarketos1.brixit.nl/postmarketos/master]
v20210212-1888-g8d13881363 [http://dl-cdn.alpinelinux.org/alpine/edge/main]
v20210212-1887-gdacf38ceed [http://dl-cdn.alpinelinux.org/alpine/edge/community]
v20210212-1891-ga4e5f5a972 [http://dl-cdn.alpinelinux.org/alpine/edge/testing]
OK: 19008 distinct packages available

~ $ sudo apk upgrade
ERROR: unable to select packages:
  uboot-tools (virtual):
    provided by: u-boot-tools
    required by: device-pine64-pinephone-0.21-r0[uboot-tools]

This is trivially dealt with by the following incantation:

~ $ sudo apk add u-boot-tools
OK: 767 MiB in 423 packages

After which the upgrade proceeds without problem:

~ $ sudo apk upgrade
(1/131) Upgrading musl (1.2.2-r1 -> 1.2.2-r2)
(2/131) Upgrading busybox (1.33.0-r2 -> 1.33.0-r4)
Executing busybox-1.33.0-r4.post-upgrade
(3/131) Upgrading alpine-baselayout (3.2.0-r9 -> 3.2.0-r11)
... etc. etc. ...

While most of our users are likely capable of figuring this out, it is an unnecessary barrier to entry, and should be dealt with.