@BenjaminHan
The important thing here with elevated temperatures on race day is to accept to not be able to run the pace and time one has hopped for to be able to do and just start with a slower pace right from the beginning (and say goodbye to the ego during warm up).
This will make the race still pleasant, and will avoid a lot of suffering at the end. But most importantly it will also allow for a faster recovery. And then maybe another attempt for a PB or BQ in the upcoming following weeks. Never wrong to have a second other marathon booked 4-5 weeks after the A goal marathon for another chance if things don’t work out.
Many years ago, wife ran the Stockholm marathon at 25C and more. She started directly conservatively with a pace 15s slower than initially planned (she was a sub 3h10min runner). Though it was her slowest marathon (3h26min) she did not suffer at all, enjoyed passing all the people (who went out too fast without considering the heat) in the last 10K and could even increase the pace a bit towards the end.
Heat over 20C == give up on initial pacing plans right from the beginning.
I ran my 3 fastest sub 2:50 marathons always in October (Frankfurt and Chicago). 5C-8C at the start and 10-12C towards the finish. Perfect conditions for PBs.
I did never ran a warm weather marathon at real race pace and pushed it there. It never made sense to me to sacrifice performance, energy and recovery during those conditions. Either I took it really easy or I intentionally DNF:ed them at 26-34K using them just as an assisted somewhat faster long run.
https://www.runnersworld.com/training/a65351982/heat-impact-on-running-pace/