As a novice in the industry, I just had a 5kW "must " inverter installed. After just 29 days it just died, leaving me now for a week without solar energy. (fighting already for a week for a replacement unit)

Any clone is of totally unknown quality. Though I got the impression that Must is one of the larger manufacturers that started off copying several Voltronic Power designs, then gradually refined them into their own products with unique capabilities.

So this might be an outlier; any manufacturer can have "early bathtub" failures.

Though I wonder if the chip shortage is tempting the shadier manufacturers to use parts of doubtful origin, or perhaps even parts of known-inferior specification (e.g. failed only some high temperature tests).