Mostly IoT devices out in the field. The ones that stopped working are running openwrt versions with an older 1.0 openssl. There is no way to update them unless I can give them some way to communicate again, even temporarily as you said.
Does anyone know of an SSL provider that would still provide the old method?
Does anyone know how I can install this ISRG Root X1 trust anchor? I can do the work such as changing anything on the server or adding a file, etc, but am not familiar enough with SSL to know most of what you are suggesting.