Toyota's idea of using both port fuel injection + direct injection to limit fuel dilution may not be working well in the cold weather.
The fuel dilution thinning the oil to a grade below 0W-16 is concerning, since Toyota recommends 10k OCI in these engines.
For a significant portion of the 10K OCI, the oil might be a grade below 0W-16. The long term engine wear from that could be an issue, especially after 100k miles in an 8 passenger minivan which will be under heavy load for a lot of its life.
If I owned a 2021 Toyota Sienna, I would check the owner's manual for the same engine in Europe or Australia. If 5W-30 is allowed for the same engine in those regions, I would use it, and do 4k OCI. That might help mitigate this issue and allow these vans to go 300k miles like the older Sienna's.