Inaction of co

You can take legal action as per provisions of law for getting the grievances rdressed properly as per law.

Jamabandhi is land records of a revenue estate prepared every 5 years by Patwari of the village and authenticated by Tehsildar, isn't it ?

What do you mean by "unlocking my jamabandi", how it is locked and who is compentent authority ?

Local abbreviations / laws apply to the facts vis-a-vis query.

It is better to consult a local prudent lawyer for proper appreciation of facts / documents, analyses, professional advise and necessary proceeding.

This matter pertains to Bihar. I am an Advocate and the land in question is my own. The opposite party has fraudulently obtained Maapi by falsely showing a third person as owner and is attempting encroachment. Correction of my land details—necessary for lawful Maapi—can be done only through Parimarjan Plus, but the Circle Officer is deliberately not unlocking my Jamabandi on the Bihar Bhumi portal, thereby aiding the encroachment.

No action has been taken on my application for unlocking Jamabandi. The continued inaction of CO appears deliberate to let Section 144 lapse and benefit the opposite party. Once 144 is lapsed opposite party will enchroach my land.

I wish to move to High court for that I need guidance.

Action I already took:
initiation of Section 144 CrPC, filing of Maapi appeal, and seeking relief under the Bihar Land Dispute Resolution Act, 2009, All these matter are in process. Once 144 is lapsed opposite party will enchroach my land.

If it is a delberate attempt by the authorities concerned by favoring the opposite parties and are reluctant to entertain your request for desired amendments to the land revenue records, you may have to issue a notice under section 80 CPC and then proceed with a suit for mandatory injunction against the authority to direct them to unlock the jama bandi records as well as permanent injunction against them to restrain them from changing the land revenue records in favor of the opposite parties without following the due process of law. 

You can add the opposite party as another defendant and can seek the relief of injunction against them to restrain them from interfering with your possession and enjoyment of the property

High court may not entertain the writ relief if there is a remedy available through lower civil court, therefore you may take action as suggested or at least consult experienced lawyers in the local in this regard and proceed as advised. 

Have you taken up the issue with the higher authorities?