Please check if emmc is working now better now
$ mount | grep blk2
/dev/mmcblk2p29 on /mnt type f2fs (rw,relatime,lazytime,background_gc=on,nogc_merge,discard,discard_unit=block,user_xattr,inline_xattr,acl,inline_data,inline_dentry,flush_merge,barrier,extent_cache,mode=adaptive,active_logs=6,alloc_mode=default,checkpoint_merge,fsync_mode=posix,memory=normal,errors=continue)
[oem@manjaro-arm ~]$ sudo dd if=/dev/zero of=/mnt/foo.file bs=1M count=1000 oflag=direct status=progress
993001472 bytes (993 MB, 947 MiB) copied, 13 s, 76.4 MB/s
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB, 1000 MiB) copied, 13.7345 s, 76.3 MB/s
[oem@manjaro-arm ~]$ time sudo md5sum /mnt/foo.file
e5c834fbdaa6bfd8eac5eb9404eefdd4 /mnt/foo.file
real 0m5.915s
user 0m0.015s
sys 0m0.039s
[oem@manjaro-arm ~]$