Dlink DWR 921 C3 JBoot back to OEM problems

This router is giving lots of issues.
After I drop the use of the 4G I'm just trying to setup port forwarding, but seems to not work.

I'd like to check if port forwarding works with OEM firmware but I can't go back to it.

I can access JBoot recovery (https://openwrt.org/toh/d-link/d-link_dwr-921#jboot_web_recovery_service)
But only flash OpenWRT by curl option (web interface does nothing after upload)
OEM firmware by curl loading seems to load but get stuck on restart (tried also unplugging the power cable), the signal led blinks in red.

Do you have any suggestions?
Do you also know how to downgrade OpenWRT?
With a previous version (still a 18.x kind) port forwarding was working, I'd like to try it.