Is it permissible to use the Gregorian calendar instead of the Hijri calendar, especially on Islamic websites that are supposed to adopt the Hijri calendar?

We write only the Hijri date on the website, and add the Gregorian date on some internal pages. There is no doubt that the original is to write the date in Hijri, and some فقهاء (jurists), such as Imam Ahmad and Ibn Uthaymeen, disliked dating by non-Arabic months. However, given the widespread use of the Gregorian calendar and the common affliction it represents, there is no harm in writing it alongside the Hijri date, provided that the Hijri date is presented first.

Using the Gregorian calendar is not considered haram (forbidden), but it is blameworthy to deviate from the Hijri calendar and suffice with the Gregorian one.

The calculation of lunar months must be relied upon for شرعية ( শরعي) matters such as Zakat, Hajj, and Iddah.