The phrase "almost all activity" is correct and usable in written English.
It can be used to describe a situation where the majority of actions or events are being referred to, but not every single one.
Example: "During the summer months, almost all activity in the park revolves around outdoor sports and picnics."
Alternatives: "nearly all actions" or "most activities".
Almost all activity was cancelled by the main political parties until after the funeral.
HH: Local solar time was fine, when almost all activity was local!
The Irish Republican Army appears to have stopped almost all activity since it declared an end to its armed campaign in July, according to a report by the independent agency that monitors paramilitary groups in the province.
Representative Nancy Pelosi, the speaker of the House, led a bipartisan Congressional delegation on a visit here on Friday, a day when almost all activity except prayer — and food distribution — had ground to a halt.
Without security, there can be no development: the UN, and most aid organisations, have ceased almost all activity in south and south-eastern Afghanistan, where lawlessness is at its worst.
For nearly half a century, Cuba was run as a command economy, with almost all activity controlled by the state.
r PsGrx showed 65.0% of its activity after incubation at 40°C for 20 min while lost almost all the activity after incubation at 50°C for 30 min.
My staff almost all have an activity that they run in or out of school out of choice; they follow their passions in some aspect of their lives.
In reality, almost all activities (including communication) require the creation and maintenance of networks of staff and allocation of resources.
He loves almost all activities (as long as they aren't crafty) and I knew he would just need time to get over the initial nervousness that any new experience would give him.
The Diagnostic and Statistical Manual of Mental Disorders says, for a person to be diagnosed with Major Depressive Disorder, they need to experience "Depressed mood most of the day, nearly every day" or "markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day" for a period of two weeks.
