Linux will also use swap in cases where there you are running processes that need more memory than you have, if that is what you mean.
Swap is not just for when you run out of RAM, though. Sometimes applications will map memory directly to swap for example. Swap can also make your RAM more efficient (memory - Do I need swap space if I have more than enough amount of RAM? - Unix & Linux Stack Exchange). For these reasons, you should always have a swap device set up.
In the case of Garuda Linux, zram has been enabled by default so your system can use compressed RAM for a swap device. This is faster than a swap partition or swap file, and spares unnecessary writes to the disk so in most cases is better. In many cases, the zram is more than sufficient for a swap device and setting up a swap file or swap partition is not necessary.
Zram does ask a little more from your CPU (to compress and extract the pages), but any relatively recent CPU should be up to the task. No garuda-inxi has been posted so you will have to make that determination on your own.
Depending on how much RAM you have and how much memory the processes run, you may need a swap file set up in addition to zram. Again, no garuda-inxi has been posted and we don’t know if you frequently run out of memory or not so you will have to figure that out on your own.
If you want to set up hibernation, you will need a swap partition or swap file in addition to zram because hibernation will not work on zram.
You can split a disk into multiple partitions with Btrfs just like any other filesystem, but there is less benefit for this practice when you are using Btrfs because you can split the disk into separate subvolumes instead. This allows you to segregate different parts of your disk without breaking the filesystem into multiple pieces, and also allows each segment to expand in size as needed (without needing to worry about a particular partition becoming full, while a neighboring one has extra space).
Subvolumes also allow you to reinstall your whole system if you’d like while keeping /home or other subvolumes from the old system intact, such as is described in this thread:
In this way, you can reinstall your system like you described without worrying about taking down your games or any other data you wish to keep.