Is it permissible for me to shorten and combine prayers when the distance I travel is 86 km, knowing that I have been working in Cairo for 10 years?

A traveler is permitted to avail themselves of the concessions of travel, such as combining and shortening prayers, so long as they do not intend to stay for four days or more in the country they have traveled to. This is the view of the majority of scholars. Combining prayers is permissible for a traveler unconditionally according to the Shafi'is and Hanbalis. If a traveler combines Dhuhr and Asr prayers by performing them early (taqdim) at their workplace, then returns to their city before the time for Asr, they are not required to repeat the prayer because their prayer was validly performed.

There is no difference in the ruling between praying individually or in congregation, but it is recommended to be diligent in praying in congregation. If you predominantly believe that you will return to your city before the time of the second prayer, it is preferable to refrain from combining prayers to avoid scholarly disagreement, as performing prayers separately is better than combining them.

If you pray Dhuhr and Asr as two rak'ahs with a single intention (i.e., intending them as one prayer), this is not permissible by scholarly consensus, and you must repeat these prayers. However, if you pray each prayer as two separate rak'ahs, then the prayer is valid.