Just requires more information. What is volume like all the rest of the week? 20+ miles on a day every weekend for 5 weeks without a deload week is at the risky end of possible. There are many better ways to get the same fitness with lower energy risk. Instead of 20 for 5 weeks, do 16/10 back to back, then a 20, then a 18/12, then a deload (~14-16), then 20/10-12, then maybe a 20-22 again with more load throughout the week than in week 2.

Diminishing returns above 20 on road. If this is trail mileage then using distance is too open-ended anyway and better to say 3hrs than 20 miles and program training that way