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I'm looking for a single word which may describe that a given process is overly formal in a sense it requires plenty of steps or involves myriad of subprocesses. For instance some company is about to introduce a new development methodology and employees complain that this methodology is ??? and therefore it would be tiresome to follow it due to the fact it has many phases. The word ceremonial I think has a religious connotation. Another option is to merely use overly/exceedingly/very to emphasize this fact but it would nice if there exists a single word.

... employees complain that this methodology is byzantine!

byzantine OED
adj. often not capitalized M-Webster

Reminiscent of the manner, style, or spirit of Byzantine politics; intricate, complicated; inflexible, rigid, unyielding.

Also as in:

Another problem facing the technology companies is the Byzantine
nature of today’s online advertising. WSJ Feb 17, 2018

Byzantium (now Istanbul) was filled with mystics, wars, and political infighting-and the word Byzantine became synonymous with anything characteristic of the city or empire, from architecture to intrigue.

labyrinthine

Oxford Living Dictionaries gives the following definition:

1 (of a network) like a labyrinth; irregular and twisting.

‘labyrinthine streets and alleys’

1.1 (of a system) intricate and confusing.

‘labyrinthine plots and counterplots’

‘In the process, he unravelled the labyrinthine means by which a
painting bought by war profiteers and sold to German army looters
found its way into the cultural heart of Britain.’

‘For a show that has the labyrinthine, seemingly nonsensical plots of
a soap opera, that's a real accomplishment.’

‘The country's legendary bureaucracy is as labyrinthine as ever, and
its legal system opaque, with separate laws for foreign and domestic
investors.’

‘The labyrinthine diplomacy and politics of the Italian wars are the
real subject of this painstaking book about what Jem meant to others.’

...

Labyrinthine, through its maze analogy, suggests unnecessary complexity and a process that could be made much more simple.

In almost all cultures and countries on this planet, what you're describing would simply be called bureaucracy and a process that involves a lot of bureaucracy would be referred to as a bureaucratic process. Here's one of the several definitions of this term from Cambridge Dictionary:

complicated rules, processes, and written work that make it hard to get something done

Example sentence (taken from the English Oxford Living Dictionaries):

More than 3,600 staff will be given the chance to influence the way the trust is run by pointing out the unnecessary rules, paperwork and bureaucracy which slow them down.

By the way, the corresponding idiomatic term for bureaucracy would be red tape. And believe it or not, it can be a single word if you properly hyphenate it and use it as an adjective: red-tape procedures. Here's how they describe this expression in Wikipedia:

Red tape is an idiom that refers to excessive regulation or rigid conformity to formal rules that is considered redundant or bureaucratic and hinders or prevents action or decision-making. It is usually applied to governments, corporations, and other large organizations.

Onerous is defined by Oxford Dictionaries as:

(of a task or responsibility) involving a great deal of effort, trouble, or difficulty.
‘he found his duties increasingly onerous’

And by Google as:

(of a task, duty, or responsibility) involving an amount of effort and difficulty that is oppressively burdensome.

Cumbersome would be a simple word to use here. In your context, cumbersome would mean something that is slow or complicated, and therefore inefficient.

Usage example -
'Most of the employees were vexed with their company's cumbersome procedures'

red tape is defined by Merriam-Webster (https://www.merriam-webster.com/dictionary/red%20tape) as:

Official routine or procedure marked by excessive complexity which results in delay or inaction.

Merriam-Webster example of red tape in a sentence:

You would not believe the red tape involved in getting the required permits.