[One (M7) Q&A, Help & Troubleshooting] thedramaturg:
Thank you! I did as you told, here is the whole output:

C:\Users\SK-Admin>fastboot erase cache
******** Did you mean to fastboot format this partition?
erasing 'cache'...
OKAY [ 0.596s]
finished. total time: 0.597s

C:\Users\SK-Admin>fastboot oem lock
...
(bootloader) Lock successfully...
(bootloader) mipi display off
(bootloader) mipi_dsi_cmds_tx_ext
(bootloader) pm8921_vreg_disable function, vreg_id = 38
(bootloader) pm8921_vreg_disable function, vreg_id = 1
(bootloader) TZ_HTC_SVC_DISABLE ret = 534642044 (0x1FDDFD7C)
(bootloader) Use PSHOLD to reset device.
FAILED (status read failed (Too many links))
finished. total time: 1.243s

C:\Users\SK-Admin>fastboot reboot-bootloader
rebooting into bootloader...
OKAY [ 0.034s]
finished. total time: 0.035s

C:\Users\SK-Admin>fastboot oem rebootRUU
...
(bootloader) Start Verify: 3
OKAY [ 0.147s]
finished. total time: 0.148s

C:\Users\SK-Admin>fastboot flash zip firmware.zip
target reported max download size of 1514139648 bytes
sending 'zip' (19578 KB)...
OKAY [ 2.287s]
writing 'zip'...
(bootloader) adopting the signature contained in this image.
(bootloader) signature checking...
(bootloader) zip header checking...
(bootloader) zip info parsing...
(bootloader) checking model ID...
(bootloader) checking custom ID...
(bootloader) checking main version...
(bootloader) checking hboot version...
(bootloader) start image[hboot] unzipping for pre-update che
(bootloader) start image[hboot] flushing...
(bootloader) signature checking...
(bootloader) [RUU]WP,hboot,0
(bootloader) [RUU]WP,hboot,99
(bootloader) [RUU]WP,hboot,100
(bootloader) ...... Successful
FAILED (remote: 90 hboot pre-update! please flush image agai
finished. total time: 10.757s

C:\Users\SK-Admin>fastboot flash zip firmware.zip
target reported max download size of 1514139648 bytes
sending 'zip' (19578 KB)...
OKAY [ 2.288s]
writing 'zip'...
(bootloader) adopting the signature contained in this image.
(bootloader) signature checking...
(bootloader) zip header checking...
(bootloader) zip info parsing...
(bootloader) checking model ID...
(bootloader) checking custom ID...
(bootloader) checking main version...
(bootloader) checking hboot version...
(bootloader) start image[boot] unzipping & flushing...
(bootloader) [RUU]UZ,boot,0
(bootloader) [RUU]UZ,boot,11
(bootloader) [RUU]UZ,boot,23
(bootloader) [RUU]UZ,boot,34
(bootloader) [RUU]UZ,boot,46
(bootloader) [RUU]UZ,boot,59
(bootloader) [RUU]UZ,boot,72
(bootloader) [RUU]UZ,boot,84
(bootloader) [RUU]UZ,boot,98
(bootloader) [RUU]UZ,boot,100
(bootloader) [RUU]WP,boot,0
(bootloader) [RUU]WP,boot,99
(bootloader) [RUU]WP,boot,100
(bootloader) ...... Successful
(bootloader) start image[recovery] unzipping & flushing...
(bootloader) [RUU]UZ,recovery,0
(bootloader) [RUU]UZ,recovery,6
(bootloader) [RUU]UZ,recovery,12
(bootloader) [RUU]UZ,recovery,20
(bootloader) [RUU]UZ,recovery,28
(bootloader) [RUU]UZ,recovery,38
(bootloader) [RUU]UZ,recovery,44
(bootloader) [RUU]UZ,recovery,49
(bootloader) [RUU]UZ,recovery,66
(bootloader) [RUU]UZ,recovery,73
(bootloader) [RUU]UZ,recovery,78
(bootloader) [RUU]UZ,recovery,86
(bootloader) [RUU]UZ,recovery,95
(bootloader) [RUU]UZ,recovery,100
(bootloader) [RUU]WP,recovery,0
(bootloader) [RUU]WP,recovery,99
(bootloader) [RUU]WP,recovery,100
(bootloader) ...... Successful
(bootloader) start image[rcdata] unzipping & flushing...
(bootloader) [RUU]UZ,rcdata,0
(bootloader) [RUU]WP,rcdata,0
(bootloader) ...... Successful
OKAY [ 17.682s]
finished. total time: 19.971s

C:\Users\SK-Admin>fastboot reboot-bootloader
rebooting into bootloader...
OKAY [ 0.042s]
finished. total time: 0.046s

C:\Users\SK-Admin>

I chose the Recovery option and unfortunately I still get the "HTC powered by android" logo screen. Well, I am desperate now ...