Ngx Bootstrap Tooltip 10 not working with Angular 15 and Bootstrap 15

I have followed the instruction on how to display the tooltip from https://valor-software.com/ngx-bootstrap/#/components/tooltip?tab=overview, however the tooltip seems not to get shown.

Namely, the tooltip is bound to this div:

But when I hover over the div it just gets elongated:

I have been trying to solve this for hours, but with no luck. My HTML is here:

  <div class="workflow-label"
       tooltip="{{phaseStateToTooltip(phase.state)}}"
       placement="top">

and the TooltipModule.forRoot() has been loaded at the root module (with TooltipModule at the module that contains the component). Do you have any idea what might go wrong? Note that Bootstrap is included in styles.scss and that popperjs core is added to package.json.

Many thanks!