glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, Twidth, Theight, 0, GL_RGB, GL_UNSIGNED_BYTE, nullptr);

...

glBindFramebuffer(GL_FRAMEBUFFER, fbo);

glClearColor(0, 1, 1, 1);
glClear(GL_COLOR_BUFFER_BIT);
glBindVertexArray(Tvao);
glDrawArrays(GL_TRIANGLES, 0, 3);
glBindVertexArray(0);

glBindFramebuffer(GL_FRAMEBUFFER, 0);

ImGui::Begin("Viewport", nullptr);
ImGui::Image((void*)(intptr_t)texture, {Twidth, Theight}, ImVec2(0.0f, 1.0f), ImVec2(1.0f, 0.0f));
ImGui::End();