.navbar-toggler-icon

please add some more description
and add some more steps to reproduce

Anjali Mehta → made their first commit to this issue’s fork.

I'll be looking into it!

Hello, @Rar9
I've tried to reproduce the issue though the issue summary was not clearly and steps to reproduce was not properly mentioned.
But on creating the sub theme by following the steps as mentioned in the project page, I found no issues regarding the same. Not sure how you created the subtheme, but on following the steps mentioned on the theme project page the navbar toggle icon is appearing properly on my system. I've tested the same on D9 and D10 as well, on both the environment the toggler icon is appearing clearly.
Attaching a screenshot for the reference!

I think you've missed some steps, after creating the sub theme you need to run npm run watch from the theme directory so that the all the asset gets compiled via laravel mixer, and in turn it'll be loaded finally from the build directory, which will not exist if you don't build your assets and as the navbar-toggler-icon is coming from bootstrap/js/dist/collapse whose code actually resides in the node_modules directory. So to make the mapping properly you need to follow the steps.