Probably an “unintelligent” question but I added an extension and I can find no way to pin it to extensions shown. I went to brave://extensions/ and it shows enabled but there is no Pin to toolbar option.
Version 1.16.68 Chromium: 86.0.4240.111 (Official Build) (64-bit)
Description of the issue: How can this issue be reproduced?
In the pic you provided you see the jigsaw puzzle piece type icon at the end of the extensions ! Click on it you will see all the extensions you have and a pin sign next to it. Activate/click on the pin sign next to the extension you want to pin. Hope this help. As far as i could understand your issue this should do it.