[Think there was an error, so reposted the comment.]

I did some testing in Nobara and it seems like there are various things that just seem to work correctly out of the box. Most of which would not run properly on Linux Mint no matter what I tried when I was using in for ~3-4 weeks.

I have decided to keep my current win10 install and just do a single Linux distro.

Here's an updated potential setup for Win10/Nobara dual boot.

NVMe SSD:

1. Windows 10 partition (NTFS)
   • leaving already installed win10 as needed
2. Nobara Linux partition (BTRFS) -- / & /home
   • Planning on using installer defaults for /boot, /, & /home. (I believe BTRFS is the default)
3. Data & Games partition (EXT4) -- documents, games, & screenshots [connected to /home partition via symlink]
   • I have heard that EXT4 can have some advantages when running games via proton because BTRFS does not have case folding

SATA SSD:

1. Current partition (NTFS)
   • leaving it as is to perserve win10 file backups already there
2. Shared Data partition (exFAT) -- music, video files, miscellaneous files like pictures, & an easy way to transfer files between win10/Linux
   • I would like to have a partition where both OSes can read these types of files easily (and so far it does not seem that there will be any significant performance issues like)
3. Linux backups partition (EXT4/BTRFS?)
   • would like to have space to backup system files, persumably with some kind of snapshots/rollback (or something like Timeshift on Linux Mint). Not sure what setup would make the most sense for Nobara yet

Question: Does anyone have any recommendations about how large the Nobara Linux partition (/ & /home) should be?

Since I do not plan to put every type of user data on it and will put all my games on the Data & Games partition (which will the largest amount of SSD space), I imagine that I could get away with a smaller than average / & /home partition here. Of course, I do want to be careful with this since running out of space on / & /home would be a massive headache.

There shouldn't be any issues with that. Most distros handle "install side by side" situations out of the box.

Data partition probably doesn't matter. Nobara might use snapshots for updates so you can rollback, not sure, but it also shouldn't horribly break things for /home.

The thing btrfs does well is root and home can be the same partition, but different subvolumes. Technically you can even have multiple distros on a single btrfs partition by means of subvolumes, so there's no unusable wasted space.

I would do btrfs, Mint won't care about the filesystem having more features than it needs, and there's so many advantages to btrfs.

E: I might leave homes separated and explicitly share some folders you want to keep in sync. Mint's configurations could impact Nobara's configurations and vice-versa. Especially if versions of things differ, maybe Nobara will upgrade some configs and make them unusable with older packages from Mint. You can just symlink your downloads and documents and whatever to a common shared data partition or subvolume dedicated to that use case.

I have no idea about the main question, though I too am interested in the answer. I do know the format for the shared partition doesn't matter. I would go ext4 because I like it's stability and don't need btrfs's features, but use whatever you want.

You get only one boot partition (EFI partition) which contains the kernel and the initramfs for both operating systems. Then, you would create two partitions to hold the rest of each individual operating system.

Shared partitions can be ext4, but if they should be read-/writable by windows, I would recommend ntfs or exFAT.

I asked a similar question last month, there were some really detailed replies in there which you might find helpful

Pick a distro you like and single boot it. If you want to mess with alternate ones, run them in VMs.