[Nexus 7 (2013) Android Development] k23m:
Hi, thanks for your report. I think it's a DEB TWRP version/build problem. Try this:

boot your current TWRP

adb push -p twrp-3.3.1-0-deb.img /tmp/

install twrp-3.3.1-0-deb.img from the tmp folder

reboot to TWRP

adb push -p sysrepart-ultimate.zip /tmp/

install sysrepart-ultimate.zip from the tmp folder

reboot to TWRP

If something does not work, here is an alternative way:

do RESTOCK including

"Restore original partitions?" YES!

flash twrp-3.3.1-0-deb.img

boot to TWRP

install sysrepart-ultimate.zip

reboot to TWRP

Now you can install LOS and Gapps. My log for:

twrp-3.3.1-0-deb.img

lineage-18.1-20210407-UNOFFICIAL-deb.zip

open_gapps-arm-11.0-super-20210130-UNOFFICIAL_TEST.zip

- 'super' is the largest Gapps package available, but you can install a small one of course

- 1.2GB system free after the install

Installing zip file '/tmp/sysrepart-ultimate.zip'
Checking for Digest file...
##########################################
# k23m Nexus 7'13 Repartition [ultimate] #
##########################################
Creating log
Removing partitions
Creating new partitions
E:recv error on uevent
Formatting new partitions
#######################
# Operation completed #
# REBOOT NOW! #
#######################
Done processing script file

fdisk -l /dev/block/mmcblk0

22 640MiB 1440MiB 800MiB ext4 vendor
1440MiB 1480MiB 40.0MiB Free Space
23 1480MiB 2040MiB 560MiB ext4 cache
2040MiB 2048MiB 8.00MiB Free Space
24 2048MiB 2049MiB 1.00MiB misc
2049MiB 2112MiB 63.0MiB Free Space
25 2112MiB 2176MiB 64.0MiB recovery
26 2176MiB 2176MiB 0.01MiB DDR
27 2176MiB 2176MiB 0.01MiB ssd
28 2176MiB 2176MiB 0.00MiB m9kefsc
2176MiB 2240MiB 64.0MiB Free Space
29 2240MiB 2240MiB 0.03MiB metadata
2240MiB 2304MiB 64.0MiB Free Space
30 2304MiB 6400MiB 4096MiB ext4 system
31 6400MiB 29824MiB 23424MiB ext4 userdata

REBOOT!!!!!!!!

install lineage-18.1-20210407-UNOFFICIAL-deb.zip

install open_gapps-arm-11.0-super-20210130-UNOFFICIAL_TEST.zip

# Begin Open GApps Install Log
------------------------------------------------------------------
ROM Android version | 11
ROM Build ID | lineage_deb-userdebug 11 RQ2A.210405.005 eng.follow.20210407.151540 test-keys
ROM Version increment | eng.follow.20210407.151540
ROM SDK version | 30
ROM/Recovery modversion | 18.1-20210407-UNOFFICIAL-deb
Device Recovery | TWRP 3.3.1-0-f5955b1c
Device Name | deb
Device Model | Nexus 7 2013 LTE
Device Type | tablet
Device CPU | armeabi-v7a,armeabi
Device A/B-partitions | false
Installer Platform | arm
ROM Platform | arm
Display Density Used | 320
Install Type | Clean[Data Wiped]
Google Camera already installed | Clean
VRMode Compatible | false
Google Camera Compatible | true
New Camera API Compatible | false
Google Pixel Features | false
Current GApps Version | No GApps Installed
Google Camera version | Legacy
Installing GApps Zipfile | /sdcard/open_gapps-arm-11.0-super-20210130-UNOFFICIAL_TEST.zip
Installing GApps Version | 20210130
Installing GApps Type | super
Config Type |
Using gapps-config | Not Used
Remove Stock/AOSP Browser | true[default]
Remove Stock/AOSP Camera | true[default]
Remove Stock/AOSP Dialer | false[NO_DialerGoogle]
Remove Stock/AOSP Email | true[default]
Remove Stock/AOSP Gallery | true[default]
Remove Stock/AOSP Launcher | true[default]
Remove Stock/AOSP MMS App | false[NO_Messenger]
Remove Stock/AOSP Pico TTS | true[default]
Ignore Google Contacts | false
Ignore Google Dialer | true[NoRemove]
Ignore Google Keyboard | false
Ignore Google Package Installer | false
Ignore Google NFC Tag | false
Ignore Google WebView | false
Total System Size (KB) | 4131968
Used System Space (KB) | 1017060
Current Free Space (KB) | 3114908
Post Install Free Space (KB) | 1284244 << See Calculations Below
------------------------------------------------------------------
# End Open GApps Install Log