last year when I went back to Arch from Manjaro, I made a critical error. I'm not sure if I was just tired when partitioning things off or what. but I made my root only 20GB instead of the 50 that I had intended. I know in a lot use cases that'll be fine, but in mine, not so much. with steam compat taking up 1-2gb and keeping one version of pacman cache, I'm constantly getting the redline warning.
Tonight I plan on booting to live and resize my luks drive and hopefully not fuck it. and if I do? oh well...Timeshift will hopefully save me.
Remember to make sure that all the boot configs are updated correctly after the resize. It could happen that your boot manager does not find the partition to unlock after a resize