Sorry to be the bearer of bad news but there are no current plans for VALORANT to support Mac OSX. For now, to play VALORANT you'll just have to bite the bullet and free up space for bootcamp or build a Windows PC.
I do feel for you here though. I worked on porting LoL to Mac native all those years ago and have seen firsthand the development time it takes to port to / maintain Mac. As much as we'd like to reach every platform and player we have to look at where our development time is most effective for the entire playerbase.
P.S. It may be possible to buy an external Thunderbolt drive and use that for bootcamp and may be a cheaper alternative than expanding your main drive or building a PC. I've never tried it personally but a cursory search online does seem to indicate it's possible. I've only ever done bootcamp from the main disk.