The Sea People were pirates, they cannot be identified as an ethnic group.
The Sea People mentioned in the Egyptian sources consisted of roving bands of people from various places who turned to piracy. It is difficult to identify their ethnicity because they are not synonymous with any nation. Claims of their existence have been exaggerated by archaeologists.Ancient History
The Sea People are largely an invention of the archaeologist Gaston Maspero. In the 1860s, he interpreted the Egyptian inscriptions at Medinet Habu as evidence of an organized group pillaging the Mediterranean. Subsequent scholars have blamed this collective of “sea people” for the devastation in Anatolia, Mycenaean Greece, and the Levant on very scant evidence. The Ugarit texts from Syria in this period simply state there were people who “lived on ships”. There is no reason to believe this is one group of people, or that they are the same people who were in Egypt. Many different ethnic groups are listed in the inscriptions. Pirates throughout history have been drawn from multiple ethnic groups but are rarely synonymous with any particular nation. There does not need to be one event that drew the Sea People to piracy. The bronze Age did not feature ‘nations’ in the modern sense, so it is ludicrous to try and find the origin of a multi-ethnic band of raiders. The Egyptian texts are fuzzy on where the invaders were actually from, simply stating they were ‘from the north’ from ‘the islands’ and simply ‘from the sea’. The Egyptians clearly could not identify a homeland for these people and list nine different ethnicities across several texts. The Egyptian reliefs depicting the raiders rely on typical Egyptian stereotypes of barbarian foreigners in their imagery. It is naïve to trust the Egyptian sources that this was a formidable coalition of nations. It is more likely they were a rag-tag band of pirates, and the Egyptians did not really know who they were describing.  Claims of an organized coalition of Sea People rely on the Egyptian sources which cannot be trusted and cannot be applied to every other declining nation in this period. The fighters were likely pirates from nowhere in particular.
There are many plausible explanations for the homeland and identity of the Sea People. Insisting that the Sea People were "just pirates" is a cop-out answer. Some of the ethnicities mentioned in the Medinet Habu inscriptions are mentioned before the Sea People attacks which indicates at least some of them were known ethnicities to the Egyptians. Texts from Ugarit in Syria strongly support Maspero's interpretation of the texts at Medinet Habu, that there was an organized cohort of invaders in the Aegean. Although the wealth of names mentioned by the Egyptians are absent, one letter from Ugarit mentions the "Shikila people", who may be the Shekelesh in the Egyptians sources. We have no reason to doubt these were the same people when many cities in this period collapsed within years of each other across the Mediterranean. Many ideas about the origins of the Sea People are valid and supported by extensive written sources.
[P1] The Sea People are an invention of archaeologists. [P2] The Egyptian sources are not reliable and could not identify the origin of their attackers. [C] The Sea People were probably pirates, not a distinct ethnic group or nation.
Rejecting the premises
- https://www.jstor.org/stable/546252?Search=yes&resultItemClick=true&searchText=sea+people+sherden&searchUri=%2Faction%2FdoBasicSearch%3FQuery%3Dsea%2Bpeople%2Bsherden%26filter%3D&ab_segments=0%2Fbasic_search_SYC-5462%2Ftest&refreqid=fastly-default%3Af1f0cafb95484e0d7764b2169d9afc0c&seq=2#metadata_info_tab_contents4. https://hal.archives-ouvertes.fr/hal-02274889/document