You do not say what your partition scheme is. Are all distros on the same disc or on their own? Solus will require it's own => 512MB fat32 boot/efi partition or it's likely to get corrupted eventually.
From a previous post, not entirely relevant but some useful info regarding changing flags. Start at step 5
"You're in a bit of a tricky situation. Are you willing to wipe your computer to do this "right"? If yes, this is what I would do in your situation:
1 - Backup all important data
2 - Make sure you backed up all important data
3 - Running in a Solus live USB, with GParted, wipe drive by deleting all partitions. Then make an ext4 partition of whatever size you want Solus to occupy. Hit the check button to run the commands. This is a placeholder to keep Windows from recognizing the space. Keep the rest unallocated
4 - Install Windows. It will automatically use the unallocated space. Run all updates Windows wants you to run. Reboot and make sure all updates and drivers have been added
5 - Reboot to a Solus live USB, with GParted, change the flag of the Windows EFI partition to msftdata (right click the partition, select manage flags). Delete the ext4 placeholder partition. Create a 1024MB (525MB is good too) fat32 partition. Create a swap partition (I use 4 - 8 GB). Create an ext4 partition with the rest of the unallocated space. Hit check to run the commands. Change flag of the new fat32 partition to boot, esp.
6 - Install Solus to the swap and ext4 drives you just made. It should select the new fat32 drive for EFI automatically. Make sure it does. If so, hit install
7 - Update Solus (sudo eopkg up -y)
8 - In GParted, change windows fat32 partition flag back to boot, esp. (Optional: change flag of Solus EFI partition to msftdata, updates run fine and Windows won't trash it)
9 - Profit
Alternate version, things are a bit fuzzy here, be careful:
Resize the main Windows partition (basic data partition), reducing it by the amount you want to use for Solus. I think you can do this with disk manager in Windows but you may need to use GParted in Solus live. The advantage with Disk manager is Windows automatically recognizes this change. If you use GParted, Windows will have problems and it will want to self repair. Allow any repair requests Windows makes. Create partitions as outlined above in this space you just made
The biggest problem with the alternate version for me is the Solus partitions are in the middle of the Windows partitions. It's messy and ruffles my OCD. Also much harder to keep track of the partitions later.
