Tech Lead is not a standardised role, as, for example, a Scrum Master. The Tech Lead role is defined differently among companies.
What is certain is that you are in the middle, interacting with different teams and stakeholders. For example:
Devs
Business Analysts / Product Owner
Product team
QA team
Software Architects
Project Manager
The client
There is also a common ground for responsibilities/expectations that can be found in most of the companies. They are:
Unblocking the team
Mentoring
Making technical & non-technical decisions
Communicate technical & non-technical decisions
Backlog refinement