You can customize social profile settings to suit your own forum.
UBB.threads 7.7.2 Changelog from 2019-04-20
[NEW] Social Profiles have been added. They are customizable and can be enabled/disabled from within the "Control Panel > Profile Settings > Social Profiles" page. With Social Profiles, your members can display their additional contact information in their Member Profile page. Your forum's current data already in the member profiles (pre-7.7.2) will be imported in to the new system upon upgrading. Social Profiles are no longer hard-coded. You'll now be able to customize or remove each when they change or close doors, such as the most recent shutter of Google+.
1) "Google+" is not enabled by default. It was inserted in to the UBB.threads while 7.7.2 was still in development and it remained there as a placeholder and as an example item to be customized by the forum owner. It is currently the last item on the "Social Profiles" page listing.
Current G+ status: Defunct.
It is discontinued for consumer (personal) and brand accounts (April 2, 2019), and in maintenance mode for G-Suite enterprise accounts.
2) linkedin.com/in vs linkedin.com/company
/in is correct for individual users.
/company is used for companies.
UBB.threads allows accounts to be created with the presumption that each account represents a single person. As such, the initial setting used is /in as the default. But if you need to customize this for a more specific need, or require a different or additional variations of the URL for your member accounts representing users vs member accounts representing companies, you can also do that within the "Social Profiles" page.
3) Instagram is already setup within UBB.threads. If you are not seeing it on your Member Profiles pages, either your member has not added their Instagram user name to their forum profile, or it is not enabled. If you choose to enable it for your users, go to Control Panel > Profile Settings > Social Profiles. It is number two on the list.