[Magisk] 7wells:
Hello, I cannot flash Magisk from TWRP, as the device is encrypted, but TWRP cannot decrypt the /data partition (known bug, and there is nothing that I can do about it). Is there a workaround for flashing Magisk? I know that flashing via fastboot a boot.img modified by Magisk is an alternative, but for this (to my understanding), I would need Magisk & Manager working on the device, which I have not (running in circles). The No space left on device messages are due to the missing /data partition, I guess. Besides, there is a java.io.IOException, which I do not understand. See /tmp/recovery.log for details:

I:Set page: 'install'
I:Set page: 'flash_confirm'
I:Set page: 'flash_zip'
I:operation_start: 'Flashing'
Installing zip file '/sdcard/Magisk-v20.4.zip'
Checking for Digest file...
I:Update binary zip
I:Extracting updater binary 'META-INF/com/google/android/update-binary'
I:Zip does not contain SELinux file_contexts file in its root.
I:Legacy property environment not used in updater.
2034+0 records in
2034+0 records out
2082816 bytes (2.0MB) copied, 0.055394 seconds, 35.9MB/s
1410+1 records in
1410+1 records out
1443916 bytes (1.4MB) copied, 0.030429 seconds, 45.3MB/s
Archive: /sdcard/Magisk-v20.4.zip
inflating: META-INF/com/google/android/update-binary
inflating: META-INF/com/google/android/updater-script
inflating: arm/magiskboot
inflating: arm/magiskinit
inflating: arm/magiskinit64
inflating: chromeos/futility
inflating: chromeos/kernel.keyblock
inflating: chromeos/kernel_data_key.vbprivk
inflating: common/addon.d.sh
inflating: common/boot_patch.sh
inflating: common/magisk.apk
inflating: common/util_functions.sh
inflating: x86/magiskboot
inflating: x86/magiskinit
inflating: x86/magiskinit64
inflating: META-INF/MANIFEST.MF
inflating: META-INF/CERT.SF
inflating: META-INF/CERT.RSA
***********************
Magisk 20.4 Installer
***********************
mount: can't find /data in /etc/fstab
- Mounting /system
- Device is system-as-root
- Mounting /apex/com.android.conscrypt
- Mounting /apex/com.android.media
- Mounting /apex/com.android.media.swcodec
- Mounting /apex/com.android.resolv
- Mounting /apex/com.android.runtime
- Mounting /apex/com.android.tzdata
- System-as-root, keep dm/avb-verity
- Encrypted data, keep forceencrypt
- Target image: /dev/block/mmcblk0p6
- Device platform: arm
- Constructing environment
- Adding addon.d survival script
java.io.IOException: DER length more than 4 bytes: 44
at a.s92.a(Unknown Source:101)
at a.s92.a(:21)
at a.s81.<init>(Unknown Source:8)
at a.v3.a(Unknown Source:69)
at a.a.main(:1)
- Unpacking boot image
Parsing boot image: [/dev/block/mmcblk0p6]
HEADER_VER [0]
KERNEL_SZ [4933624]
RAMDISK_SZ [771101]
SECOND_SZ [0]
EXTRA_SZ [0]
OS_VERSION [10.0.0]
OS_PATCH_LEVEL [2020-09]
PAGESIZE [2048]
NAME []
CMDLINE [console=ttyHSL0,115200,n8 androidboot.hardware=mako lpj=67677 user_debug=31 vmalloc=340M buildvariant=userdebug]
CHECKSUM [xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx000000000000000000000000]
KERNEL_FMT [raw]
RAMDISK_FMT [gzip]
- Checking ramdisk status
Loading cpio: [ramdisk.cpio]
- Stock boot image detected
cat: write error: No space left on device
- Patching ramdisk
sh: write error: No space left on device
sh: write error: No space left on device
sh: write error: No space left on device
sh: write error: No space left on device
Loading cpio: [ramdisk.cpio]
Add entry [init] (0750)
Patch with flag KEEPVERITY=[true] KEEPFORCEENCRYPT=[true]
Loading cpio: [ramdisk.cpio.orig]
Record new entry: [apex] -> [.backup/.rmlist]
Record new entry: [debug_ramdisk] -> [.backup/.rmlist]
Record new entry: [dev] -> [.backup/.rmlist]
Record new entry: [fstab.mako] -> [.backup/.rmlist]
Record new entry: [init] -> [.backup/.rmlist]
Record new entry: [mnt] -> [.backup/.rmlist]
Record new entry: [proc] -> [.backup/.rmlist]
Record new entry: [sys] -> [.backup/.rmlist]
Create directory [.backup] (0000)
Add entry [.backup/.magisk] (0000)
Dump cpio: [ramdisk.cpio]
- Repacking boot image
Parsing boot image: [/dev/block/mmcblk0p6]
HEADER_VER [0]
KERNEL_SZ [4933624]
RAMDISK_SZ [771101]
SECOND_SZ [0]
EXTRA_SZ [0]
OS_VERSION [10.0.0]
OS_PATCH_LEVEL [2020-09]
PAGESIZE [2048]
NAME []
CMDLINE [console=ttyHSL0,115200,n8 androidboot.hardware=mako lpj=67677 user_debug=31 vmalloc=340M buildvariant=userdebug]
CHECKSUM [xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx000000000000000000000000]
KERNEL_FMT [raw]
RAMDISK_FMT [gzip]
Repack to boot image: [new-boot.img]
write failed with 2: No such file or directory
! Unable to repack boot image!
- Unmounting partitions
Updater process ended with ERROR: 1
I:Install took 8 second(s).
Error installing zip file '/sdcard/Magisk-v20.4.zip'
Updating partition details...
...done
Unable to mount storage
I:Set page: 'flash_done'
I:operation_end - status=1

Thanks for your help!