Déplacer les tables semble être un objectif simple, pourtant il faut rester prudent pour éviter les accidents.

Yes. In French, an infinitive can act as the subject of a sentence.

• Déplacer les tables = moving the tables / to move the tables
• This whole infinitive phrase is the thing that seems simple.

So:

• Déplacer les tables semble être un objectif simple
  literally: Moving the tables seems to be a simple objective

English often prefers moving the tables here, while French is very comfortable using the plain infinitive.

Les tables usually refers to specific tables already known from the context, or to the tables involved in the situation.

• les tables = the tables
• des tables = some tables

So:

• Déplacer les tables = moving the tables
• Déplacer des tables = moving some tables

Both are grammatical, but they do not mean exactly the same thing.

Semble être means seems to be.

• semble = seems
• être = to be

So:

• semble être un objectif simple = seems to be a simple objective

French can often omit être after sembler when an adjective follows directly:

• Cela semble simple = That seems simple

But here the complement is a noun phrase:

• un objectif simple

That is why être is used naturally:

• semble être un objectif simple

It is grammatical, but depending on context, it may sound a little formal or slightly unusual.

Objectif means goal/objective, so un objectif simple suggests:

• a simple goal
• a straightforward aim

If the idea is more about the action itself being easy, French might often prefer something like:

• une tâche simple = a simple task
• une opération simple = a simple operation
• quelque chose de simple = something simple

So the original sentence is correct, but a learner should know that objectif emphasizes the goal, not just the practical task.

Pourtant means however, and yet, or nevertheless.

It introduces a contrast:

• It seems simple,
• yet you still have to be careful.

So:

• ..., pourtant il faut rester prudent...
  = ..., yet one must remain careful...

Compared with mais:

• mais = but
• pourtant = however / and yet / nevertheless

Pourtant often sounds a little stronger or more expressive than mais, especially when the second part goes against what you might expect from the first.

Il faut is an impersonal expression meaning:

• it is necessary
• one must
• you have to

In this sentence:

• il faut rester prudent = you have to remain careful / one must stay cautious

The il here does not refer to a person. It is just the fixed grammatical subject used in this expression.

Very common pattern:

• Il faut + infinitive

Examples:

• Il faut attendre. = One must wait.
• Il faut partir. = We/you/one have to leave.

Both can make sense, but rester prudent adds the idea of continuing to be careful or staying cautious.

• être prudent = to be careful
• rester prudent = to remain/stay careful

Here, rester prudent suggests that even if the task looks easy, you should keep a cautious attitude throughout.

So it is a very natural choice.

Because rester is a linking verb, and linking verbs are followed by an adjective, not an adverb.

• prudent = careful, cautious → adjective
• prudemment = carefully, cautiously → adverb

So:

• rester prudent = to remain cautious
• not rester prudemment

If you wanted an adverb, you would use a different kind of verb, for example:

• agir prudemment = to act cautiously
• avancer prudemment = to move forward carefully

It agrees with the understood subject of rester, which is a general, unspecified person: one / you / people in general.

In that kind of generic statement, French commonly uses the masculine singular as the default form:

• il faut rester prudent

This does not mean the sentence is only about a man. It is a general statement.

If the subject were clearly plural or feminine, agreement could change in other contexts. But in this impersonal construction, prudent is normally left in the default masculine singular form.

Pour + infinitive is a very common French structure meaning in order to or to.

• pour = in order to / to
• éviter = to avoid

So:

• pour éviter les accidents = to avoid accidents

This is how French usually expresses purpose when the subject stays general or the same.

Examples:

• Il travaille pour réussir. = He works to succeed.
• Ferme la porte pour éviter le bruit. = Close the door to avoid the noise.

French usually needs an article before a plural noun in this kind of sentence.

• les accidents = accidents / the accidents

In English, we can often say simply avoid accidents with no article. French normally does not do that. It prefers:

• éviter les accidents

Here les has a general meaning: accidents as a category, not necessarily some specific accidents already mentioned.

So this is a very common difference between French and English.

The main verbs are in the present tense:

• semble = present of sembler
• faut = present of falloir

The other verbs are infinitives:

• déplacer
• être
• rester
• éviter

So the sentence combines:

• present-tense main verbs
• infinitive verb phrases

This is very common in French.

Yes. The original sentence is correct, but a few alternatives may sound more natural depending on context.

For example:

• Déplacer les tables semble simple, pourtant il faut rester prudent pour éviter les accidents.
• Déplacer les tables paraît simple, pourtant il faut rester prudent pour éviter tout accident.
• Même si déplacer les tables semble simple, il faut rester prudent pour éviter les accidents.

A learner should know that the original is valid, but native speakers might sometimes choose a slightly lighter phrasing, especially by dropping être un objectif and saying simply semble simple.