too_many_libs.cpp

// lib A
Global Server;

void on(const Uri &uri, HTTPMethod method, THandlerFunction fn, THandlerFunction ufn);

server->on("/", std::bind(&myClass::handler, this, handlerArg));

void myClass::handler(bool arg){
    Server->blargh();
}

// lib B
Global Server (async)

AsyncCallbackWebHandler& on(const char* uri, WebRequestMethodComposite method, ArRequestHandlerFunction onRequest, ArUploadHandlerFunction onUpload, ArBodyHandlerFunction onBody);

server->on("/", std::bind(&myClass::handler, this, std::placeholders::_1, handlerArg));

void myClass::handler(AsyncWebServerRequest *request,bool arg){
    request->blargh();
}