Hi Bohdan,
What you need is show personalized view or dashboard of activities based on opportunity, right?
You can go Settings > Customization > Customize the system > Entities > Activity > Views to create a new view.
Add columns of activity entity you need firstly, and ‘Regarding’ field is must.
Then select ‘Regarding(opportunity)’ in record type, add fields of opportunity entity you need.

click ‘Edit Filter Criteria’ button to set filter to make the view just show activities that regarding type is opportunity.

save and publish all customization, go to the view and select you just crested, the view will show records that regarding type is opportunity.

if you want to show records based on one specify opportunity, you can expand 'topic(Regarding)' column and click filter by to insert opportunity name you need.

and you can add the view you created to the dashboard, but if you want to filter column in dashboard, you need enable editable control.

Regards,
Leah Ju
Please mark as verified if the answer is helpful. Welcome to join hot discussions in Dynamics 365 Forums.