Your fastboot skipped multiple files lol. Are you using some 5yo fastboot version or something...?I started off clean, since I had to use the MSM tool. Let the phone update in OOS, then followed the instructions. I just get dumped off at the bootloader (I did format data).
ohioyj@GamingDesktop:~/Desktop/flash$ sudo fastboot boot recovery.img
downloading 'boot.img'...
OKAY [ 0.332s]
booting...
OKAY [ 0.080s]
finished. total time: 0.412s
ohioyj@GamingDesktop:~/Desktop/flash$ sudo fastboot update lineage-18.1-20210112_053040-UNOFFICIAL-kebab.zip
extracting android-info.txt (0 MB)...
extracting boot.img (96 MB)...
target reported max download size of 268435456 bytes
archive does not contain 'boot.sig'
archive does not contain 'boot_other.img'
extracting dtbo.img (24 MB)...
archive does not contain 'dtbo.sig'
archive does not contain 'dt.img'
extracting recovery.img (96 MB)...
archive does not contain 'recovery.sig'
extracting system.img (963 MB)...
archive does not contain 'system.sig'
archive does not contain 'system_other.img'
extracting vbmeta.img (0 MB)...
archive does not contain 'vbmeta.sig'
extracting vendor.img (969 MB)...
archive does not contain 'vendor.sig'
archive does not contain 'vendor_other.img'
--------------------------------------------
Bootloader Version...: unknown
Baseband Version.....:
Serial Number........: (removed)
--------------------------------------------
sending 'boot_b' (98304 KB)...
OKAY [ 3.445s]
writing 'boot_b'...
OKAY [ 0.389s]
sending 'dtbo_b' (24576 KB)...
OKAY [ 0.866s]
writing 'dtbo_b'...
OKAY [ 0.095s]
sending 'recovery_b' (98304 KB)...
OKAY [ 3.479s]
writing 'recovery_b'...
OKAY [ 0.280s]
sending sparse 'system_b' 1/4 (259064 KB)...
OKAY [ 9.501s]
writing 'system_b' 1/4...
OKAY [ 0.570s]
sending sparse 'system_b' 2/4 (258272 KB)...
OKAY [ 9.420s]
writing 'system_b' 2/4...
OKAY [ 0.420s]
sending sparse 'system_b' 3/4 (258272 KB)...
OKAY [ 9.452s]
writing 'system_b' 3/4...
OKAY [ 0.403s]
sending sparse 'system_b' 4/4 (210844 KB)...
OKAY [ 7.667s]
writing 'system_b' 4/4...
OKAY [ 0.369s]
sending 'vbmeta_b' (8 KB)...
OKAY [ 0.002s]
writing 'vbmeta_b'...
OKAY [ 0.004s]
sending sparse 'vendor_b' 1/4 (262140 KB)...
OKAY [ 9.427s]
writing 'vendor_b' 1/4...
OKAY [ 0.539s]
sending sparse 'vendor_b' 2/4 (262140 KB)...
OKAY [ 9.511s]
writing 'vendor_b' 2/4...
OKAY [ 0.545s]
sending sparse 'vendor_b' 3/4 (262140 KB)...
OKAY [ 9.576s]
writing 'vendor_b' 3/4...
OKAY [ 0.549s]
sending sparse 'vendor_b' 4/4 (206256 KB)...
OKAY [ 7.277s]
writing 'vendor_b' 4/4...
OKAY [ 0.347s]
Setting current slot to 'b'...
OKAY [ 0.033s]
rebooting...
finished. total time: 84.322s
ohioyj@GamingDesktop:~/Desktop/flash$