It is possible to work collaboratively on a single branch, if that is sufficient for your particular use case! You'd be able to preview and test any apps on this branch before merging into main.
That said, I do think taking the time to spin up a new Space is probably worth the time investment. It's a fairly painless process on Cloud and just a little more complicated otherwise due to the requisite DNS configuration.
Once you've created the new space, all you need to do to get up and running is configure SCM and point it to a separate branch.
For example, I have an instance at toula.retool.com that is pointed towards the main branch in my remote GitHub repository and a separate Space at dev.toula.retool.com that is pointed towards the dev branch in the same repository.