Object is possible 'null' compiler error even when verifying variable - TypeScript [duplicate]

As you can see in the code snippet below, a certain React element should be shown according to a variable of value type boolean. However, even when checking if the selectedRepository is truthy and coercing it to a Boolean, the TS compiler gives the error Object is possibly 'null'

{...}
  const shouldShowRepositoryDetails = !isLoading && Boolean(selectedRepository);

  return (
    <Layout header={<RepositoryDetailsHeader />}>
      {shouldShowRepositoryDetails && (
        <RepositoryDetailsContainer>
          <header>
            <img
              src={selectedRepository.owner?.avatar_url}
              alt={selectedRepository.owner?.login}
              aria-label={selectedRepository.owner?.login}
              title={selectedRepository.owner?.login}
            />

            <div>
              <strong>{selectedRepository.full_name}</strong>
              <p>{selectedRepository.description}</p>
            </div>
          </header>
        </RepositoryDetailsContainer>
      )}
    </Layout>
  );

I would like to understand if this is a TS issue or if someone already experienced this.