As it seems to me, this work will have been finished by tomorrow. Чому тут Future Perfect Continuous?

Тут не Future Perfect Continuous, а Future Perfect Passive.

Речення: As it seems to me, this work will have been finished by tomorrow.

Розберемо його:

will — майбутній час.

have — допоміжне дієслово для Future Perfect.

been — ознака пасивного стану.

finished — V3 (Past Participle).

Формула:

will + have + been + V3 = Future Perfect Passive

Чому це не Future Perfect Continuous?

Формула Future Perfect Continuous інша:

will + have + been + V-ing

Наприклад:

By tomorrow, I will have been working here for five years.

By noon, they will have been waiting for three hours.

Тут після been стоїть V-ing, а не V3.

Чому в твоєму реченні пасив?

Запитай себе:

Чи "this work" виконує дію?

Ні.

Робота не може сама себе закінчити.

Її хтось закінчить.

Активний стан:

They will have finished this work by tomorrow.

Пасивний стан:

This work will have been finished by tomorrow.

Зверни увагу на останнє слово:

been finished → V3 → пасив.

been working → V-ing → continuous.

Отже:

As it seems to me, this work will have been finished by tomorrow.

це Future Perfect Passive, що означає:

Як мені здається, цю роботу буде завершено до завтра / до завтрашнього дня.