A private individual using a Huawei phone or router isn't a national security threat to the US.
However, in a broader sense, the US government sees the technological development of China as a threat to American strategic dominance, and has been taking ever more drastic measures to try to hobble the Chinese tech sector. The campaign against Huawei, which began a few years ago, was the opening shot. Blacklisting various Chinese semiconductor companies (which does not only prevent American companies from doing business with them, but which also threatens companies around the world with secondary sanctions if they do business with the targeted companies) was a further escalation. This was also justified as a "national security" measure, with the claim that these companies do business with the Chinese military (these claims were not publicly backed up by evidence, of course). Biden dramatically escalated the "tech war" recently with even broader sanctions against much of the Chinese high-tech sector.
The "national security" justification has become so broad that virtually any business with China is now being construed as a national security threat. Americans should consider if they really want to turn their relationship with the world's largest economy into one that is purely hostile.