This is a feature for ergonomy of use in ordering and interacting with tabs in Android mobile devices.
Using the first tab created in a new tab-group it is not possible to open the first additional tab in the to-be-formed group of tabs.
There are two options, but both lead to opening a new tab in a new tab-group: new mother-tap, which eventually become a group or a single.
Those options are: through the settings menu-> new tab or using the tab-counter double-press pup menu.
There would be a third option, that one could came up with: just pressing the tab-counter once, boing back to “cards-menu”, where all groups are displayed, and prest the mother-tab to somehow “add” inside a new children-tab. However this is only possible in tab-group that has previously created.
BTW, scrolling with an empty tab-group or mother-tap DOESN’T make appear the bottom bar of child-tab-icon with the unique tab and the [+] option. That one would be some solution.
Soulution:
Other options is adding the option both in settings and tab-counter with tab within group.
That would improve some user experience and refine the browser ergonomy in mobile devices.