Hi, I am trying to crunch some workunits on my Orange Pi 4 running Armbian Focal, kernel 4.4.213-rk399 (downgraded due to HDMI issues). Unfortunately, I immediately get this error in the stdout:

../../projects/www.mlcathome.org_mlcathome/mlds_9.61_arm-unknown-linux-gnueabihf: error while loading shared libraries: libz.so.1: cannot open shared object file: No such file or directory

The package zlib1g is already installed:

zlib1g is already the newest version (1:1.2.11.dfsg-2ubuntu1.2).
0 upgraded, 0 newly installed, 0 to remove and 77 not upgraded.

What could be the issue?
Thanks :)

Are you running a 64-bit environment? If so, try installing the 32-bit version of libz, something like: `sudo apt install zlib1g:armhf` .. that said, libz should be included in the appimage so you shouldn't need it, but worth a shot.

Thanks, after that I got:

dlopen(): error loading libfuse.so.2

AppImages require FUSE to run. 
You might still be able to extract the contents of this AppImage 
if you run it with the --appimage-extract option. 
See https://github.com/AppImage/AppImageKit/wiki/FUSE 
for more information

thus using the same logic I installed libfuse2:armhf
Now the board is crunching six workunits, we will se in few hours but I think it is working well :)

By the way, why does the scheduler download apps for both 32 bit and 64 bit in a 64 bit environment?

file mlds_9.61_a*
mlds_9.61_aarch64-unknown-linux-gnu:   ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, for GNU/Linux 3.7.0, BuildID[sha1]=51d6e77d008afa7e177385e66d5274a0b203ac54, stripped
mlds_9.61_arm-unknown-linux-gnueabihf: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=6b43dbba566d533656f6fec20677a81dde81fc1c, stripped

ps aux | grep mlds
boinc      13457 95.4  3.9 210080 155632 ?       RNl  08:57   2:51 ../../projects/www.mlcathome.org_mlcathome/mlds_9.61_arm-unknown-linux-gnueabihf -a LSTM -w 64 -b 2 -s 32 --lr 0.001 --maxepoch 192

It is working with the 32 bit app. Should I disable the 32 app manually or it is fine?

EDIT:
I remember I had added this line in cc_config.xml in order to run 32 bit WCG's workunits:

<!-- <alt_platform>arm-unknown-linux-gnueabihf</alt_platform>-->

Now it is commented, I aborted MLC's workunits, restarted the client but still the only running app is arm-unknown-linux-gnueabihf

There is no Aarch64 app, there is only a 32-bit ARM application that you can run on a 64-bit board with a 64-bit OS -as you discovered.
You might need to do more though, I'd suggest

sudo dpkg --add-architecture armhf
sudo apt update --fix-missing
sudo apt dist-upgrade
sudo apt install libc6:armhf libstdc++6:armhf zlib1g:armhf libfuse2:armhf