This update was released on the 20th October 2020. Full release announcement can be read here. https://aussieguy92.com/altspacevr-4-3-5-urp-update-now-out/
The URP Unity Upgrade update will release on Wednesday, October 20, 2021. All world builders & event hosts will need to update their content by Oct 20th to ensure content compatibility.
Thank you to our World Builder community for the preview build tests and bug reports we received, this support has been crucial to our team tracking down bugs and creating fixes. Thank you for your patience throughout this entire process, we know it has been a tough wait for many content creators.