Is it recommended to عقد الزواج (solemnize marriage) on Friday, or is that considered a bid‘ah (innovation), and what is the most preponderant opinion on this matter?

There is no specific day designated for concluding a marriage contract, and it is permissible to conclude it on any day of the week or year. The jurists of the four madhhabs have stated that it is desirable to conclude the marriage contract on Friday, citing the practice of some of the Salaf and the fact that Friday is a blessed and noble day, in which the blessing of marriage is hoped for. It should be noted that the jurists used the term "yustahabb" (desirable) and not "yusann" (sunnah) due to the lack of evidence from the Prophet, peace and blessings be upon him; rather, it is an ijtihad (independent reasoning) on their part. However, Sheikh Ibn 'Uthaymeen holds that this desirability is questionable due to its lack of proven origin from the Prophet, peace and blessings be upon him, and the correct view is that the contract is permissible whenever it is feasible, at any time and in any place.