Can't boot my mac os partition anymore

EaseUS Partition Manager is a Windows only app which only works with Windows file systems according to the product documentation. There is no mention of macOS or APFS file systems and APFS Containers, so the app only treats the macOS partition as a basic (probably empty) partition. When an app resizes a partition the app needs to also adjust the file system to match the changes which the EaseUS Partition Manager is unable to do as the product page only mentions compatibility with NTFS & FAT32 file systems. It is always very important to read all the product documentation and review the user manual to understand the limitations of any product.

Modifying partitions is always extremely risky even when using the correct app. Always make sure you have a current backup before making any major system modifications is extremely important.

Your only options are to attempt data recovery of the broken macOS partition. I'm not sure if it is possible to do so by using a Windows app...theoretically it should be possible, but that is something you will need to research unless another contributor has any personal experience.

To use a macOS data recovery app you will need to install macOS to an external USB3 drive, then boot this Mac to the external USB drive containing a full version of macOS where you can install & run a third party data recovery app. Many data recovery apps allow you to scan a system for free in order to see whether any files can be found, but you will need to pay for the app in order to actually recover the found files. I've used Data Rescue in the past. Stellar is one which I've seen mentioned on these forums as is Disk Drill, and I believe EaseUS also makes a data recovery app for the Mac which appears to be free as well. I've never personally used any of these other apps.

Another option is to contact a professional data recovery service such as Drive Savers or OnTrack. Both vendors provide free estimates and both are recommended by Apple and other OEMs. I can personally vouch for Drive Savers as our organization used them several times many many years ago and we were satisfied with their services.

Maybe there is someone local who performs data recovery, but be very careful since there are a lot of amateurs out there who may offer services, but they may not take many precautions (perhaps intentionally or perhaps through inexperience), because being cautious involves time.

Keep in mind you don't want to make any more changes to this drive, or it may make matters worse. Sometimes even running a data recovery app will make a change to the drive (sometimes without even asking), plus it is easy to accidentally choose a wrong item which introduces an unintended change to the drive. The more modifications made (intentional or accidental) may affect whether even a professional data recovery service will even be able to recover the files.

continued....

Once you have recovered your data from the macOS partition (or given up on recovering the data), then you will most likely need to erase the whole physical drive and reinstall macOS followed by reinstalling BootCamp & Windows again. Perhaps it may be possible to erase just the "unavailable" area and reinstall just macOS, but I highly recommend starting completely over since there is no way to know whether EaseUS modified the partitions correctly for macOS to be happy. As a general rule, you should only use the utilities available within the OS to modify partitions and file systems which affect an OS installation. In fact, from my limited understanding of BootCamp from reading these forums....I don't believe it is safe to adjust the partitions even using macOS tools since it would most likely make the Windows partition unbootable.

This is why I never recommend partitioning or dual booting to the same drive, although I don't believe you have much choice when using BootCamp. The safest option when wanting to run another OS is to install the second OS into a Virtual Machine, but I do understand that this is not a viable option for some workloads.

People should always have frequent and regular backups of their computer (including each OS on it) and all external media (including the cloud) which contains important & unique data. Always make sure to have a good backup before making any major system changes. Keep in mind SSDs can fail at any time without any warning signs, plus with 2018+ Macs there are a lot more ways of losing data where data recovery may not even be possible.

Writing that last bit just made me think of something else which concerns me....I hope that the "unallocated" former macOS partition still retains its data if that is an SSD, because usually if an area is not being use or assigned, then that portion of the SSD will be cleared of all data. In fact, it may actually be risky booting into macOS from an external drive (or even recovery mode) as it may trigger that portion of the SSD to zero its contents due to how SSDs work (I honestly don't know, but I would be concerned about that potentially happening). If this is a hard drive, then there is a good chance at least some of the data can be recovered, but I'm not sure if the drive is an SSD.

I've written my response both to help you to resolve the situation and to try to explain some details to help educate others who may read this post about how some of these things work.