Issue of the topic: the issue is that after changing the ISP, I cannot update or upgrade the system, nor access the openhab cloud (I do not know if this is the correct topic category, please suggest a better one if any)
the error is:
You can either change the LAN IP of the new Router (go into its admin interface) = this is better since most of your LAN devices may remember the old IP. Make sure that the old Router is offline not to create an IP Address conflict.
or change the default gateway on the rPi (assuming you have static IP set and not DHCP)
if manual IP: did you use /etc/dhcpcd.conf in the past to set it or another method?