@leocg Hi, it looks like there is an option to achieve what I was looking for.

On the first workspace, open the tabs you prefer.
On the second workspace, open different tabs.
on the third worpsace, open different tabs again.
. . . and so one.

In the browser settings, make the setup that on start up, the browser will open with the last used tabs.
That wil do for me.

@leocg that is a pitty.
it would be a very convenient feature.

Is it possible to pre-define TABS per workspace?
I can setup tabs that will be opened on startup of Opera but it appears that these tabs do appear on every workspace.
I would like to achieve the same as possible with profiles in Google Chrome: my private profile has different tabs as my professional profile.