24 port switch does not boot up after wrong firmware update

Dear all,

I bought the managed switch on ebay which was working fine in my new home Gigabit Network. After trying to update the original firmware 4.1.0.9 to the latest version, the switch did not reboot again. Netgear Support declined service since my equipment is out of warranty... not even for money. Luckily, I found some users in the community with the same problem:

https://community.netgear.com/t5/Smart-Plus-Click-Switches/GS724Tv3-does-not-boot-after-firmware-update/m-p/1192385/highlight/true#M4534

Then tried to unbrick the switch with suggested solution:

https://www.dutn.nl/repairs/reparaties_gs724t.html

I was happy, discovering that it was pretty easy to follow Duteweerd's instructions BUT when trying to flash my switch as per these instructions, I got a "connection timeout"...

There are many potential commands to try via UART but which one will be the right one?

If there is anybody out there to help me with that issue by email, telephone or within this community, I would really really appreciate that! Since I am not a real network / IT professional, I would need some instructions on how to unbrick my switch via UART...

Netgear support denied every personal service... a pity!

Thanks for every help I can get here, I do not want to dump my equipment...

Björn