## 1 Introduction  
Fifth-generation communication networks are designed to support novel advanced use cases, facilitating technologies like massive machine-to-machine communication, ultra-reliable low-latency communication (URLLC) services, or multi-access mobile edge computing solutions. One of its major use cases is the V2X--vehicle to anything--communication. In the automotive industry, V2X communication is a novel technology addressing many critical safety use cases; thus, the security and safety of the potential V2X networks is essential. In the automotive world, the faulty operation of systems can easily cause physical harm. Thus the quality of the communication channel is crucial. Apart from that, V2X communication also features different requirements than usual due to the peculiar design principles of V2X communication. The 5 GAA has three studies about several use cases, where these reports present use case descriptions and service level requirements [1; 2; 3]. In addition, the 5 GAA has several other very high-quality studies and reports in this field, such as [4], which introducessystem enablers and best practices for V2X services. Similarly, there are documents with 3 GPP support about V2X service requirements. These requirements are identified by taking into account the V2X service requirements defined by ETSI ITS and US SAE. The specification includes requirements of safety and non-safety aspects [5]. Ref. [6] provides an overview of V2X use cases, their potential outcomes, and a comparison between the potential requirements based on their categorization, i.e., latency, message size, mobility performance, response time, message frequency, anonymity, integrity, reliability, and communication. In contrast, Ref. [7] provides a survey of the latest V2X use cases, including requirements and various 5G-enabling technologies under consideration for vehicular communications. Subsequently, we first provide an interesting mapping between the three 5G pillars and V2X use case groups. While Ref. [8] outlines a series of key enabling technologies from a range of domains, such as new materials, algorithms, and system architectures, Ref. [9] provides a comprehensive overview on 5G-MEC testbeds for V2X applications. Aiming for truly intelligent transportation systems, we envision that machine learning (ML) will play an instrumental role in advanced vehicular communication and networking. Furthermore, Ref. [10] presents novel C-ITS use cases that utilize machine learning. The primary objective of this paper is to demonstrate the potential of artificial intelligence in enhancing C-ITS applications. This paper shows that C-ITS applications are built on vehicle-level, intervehicle-level, and infrastructure-level applications as well. There are several papers and studies and research about the requirements and enablers of V2X use cases--including [8] as a survey on use case requirements, ref. [11] as a survey on V2X slicing, ref. [12] as a survey on V2X cybersecurity mechanisms, or ref. [13] on C-V2X for Level 5 autonomous driving from 3 GPP standards' viewpoint, among others. Still, there is not much work that analyzes the potential controversies, obstacles, and challenges in this field. The objectives of this research paper are as follows:  
1. Identify, analyze, and extend the understanding of the key challenges related to the large-scale deployment of 5G-based cellular vehicle-to-everything (C-V2X) systems. 2. Pinpoint obstacles and controversies in the cellular V2X standards caused by special requirements. 3. Introduce the main definitions and standards in connection with C-V2X and explore RAN security and positioning. 4. Highlight influential C-V2X projects that have a significant impact on the widespread adoption of this transformative technology. By thoroughly examining these challenges, our research contributes to a comprehensive understanding of the complexities involved in the deployment of 5G-based C-V2X systems.