Need help with R7800 and Luci/wifi connections going dead

Hello,
My laptop also lost contact to LuCI after installing OpenWRT on my R7800.

My steps:
R7800 original (Stock V1.0.3.92).
I installed the 'factory' version 24.10.1 (verified hash) and
followed this to get 'AP' behavior:

After this, I checked/ticked the wan port in br-lan to include it (in 'Devices' -- needed the extra port) and
enabled wireless ..11b/g/n without configuring.
At 'save' Luci seemed to crash, blank screen in the browser.

Restarted the R7800
At that point Ipconfig showed correct IP (from DHCP ISP router), gateway and DNS.
Internet worked and there was an added Wifi 'OpenWRT' (open).
So it seemed not reaching Luci was the only issue.

Restarted the R7800 with reset, (white blinking) fixed IP4 on my HP Elitebook (192.168.1.100 - it got 169.254.239.40 from the R7800) and then connecting to 192.168.1.1 in Firefox on W10 shows a blank screen with a link:
LuCi - Lua Configuration Interface (192.168.1.1/cgi-bin/luci/), but this times out when clicked.
I am able to ping 192.168.1.1 (<1ms)

When restarting the R7800 without 'reset' it seems to boot to a continuous white light, but still only the Luci link and pinging times out ('unreachable').

I am new to OpenWRT and limited in Linux, but tried to connect via Tftpd64-4.64 (connection rejected) and PuTTY (v0.83, port 22, timed out)

My newbie questions:

  • How can I establish an SSH-client terminal connection to the R7800 to view files and try these 'firstboot' and 'reboot' commands? What SSH-client? What settings (in detail)? (maybe a link to a general introduction in SSH?)
  • How can I install the ..sysupgrade or ..uImage version through Tftp from W10 (software? settings?) and is this safe, or can I 'brick' my R7800 completely?
  • Any other topics to link to, covering this issue in more detail?

I hope to execute the 'Recovery process' as described by hnyman in nov 2016 here:

Many thanks in advance for your help,
Joep