Present continuous with adverbs

Question

Can I use present continuous with adverbs such as "often, sometimes" and so on?

1. He is often working in the garden - meaning working in that garden is a new occurrence or something temporary yet performed "often" within that time frame?

Answer 1

It means neither 'a new occurrence' nor 'temporary'.

He is often working in the garden when I walk past his house.

I walk past the house regularly, and on many of those occasions I see him at work in his garden.

Answer 2

One of the meanings of the continuous is "repeated action". In that case the marked expression, "He's often working" would emphasise the repetition.

Such use is "marked". If you are not very confident, then you should not use this or other "marked" expressions. Not because they are wrong, but because they have an odd or unsettling feeling. A skilled speaker might use "marked" expressions on purpose. But if you are an English learner, it will simply be considered to be a mistake.

Answer 3

Yes. Present Continuous Tense can also be used to talk about temporary situations (but without words meaning often).
I am staying in my brother's house for a few days.

The example OP gave, with time expressions like always, forever, constantly (which mean often), is something which happens again and again:
The puppy is always trying to chew on my slippers..
My friends are forever playing games on their mobile phones..

You will find this British Council link useful for understanding the various functions of Present Continuous Tense.

something which happens again and again:
It's always raining in London..
They are always arguing..
George is great. He's always laughing..