Innies/outies across 2-4 stacked row/column bands. hard killer only
Comparing the tinted rows/columns' 45-total against the cages leaves the marked cells, which must total 13; no assignment reaching it allows 2, 4, 5, 7 and 8 in R2C2, R4C2.
The 45-rule applied to a band of two or more adjacent rows or columns (which sum to 90, 135, ...). Larger regions often isolate a single protruding cell whose value follows immediately.