4538...9..2..4.83..7.3...4..4..36.29231..476.96527.4.331...295..94.5.3.2582..367.
This is the position after basics of the August1 posted puzzle. Cells r6c68 & r8c8 are all limited to candidates 1,8.
Does that not mean that r8c8 cannot be 1 or 8 as that would lead to multiple solutions through a Unique Rectangle?
Yogi