Stuck on High Sierra and can't update anymore

[Leon.De.La.Rosa]

On a 2018 15-inch Macbook Pro, I just forgot to keep my OS up to date and now I can't even connect to the app store, but the Monterrey Installer did download although it tells me my internal HD is not compatible with the update. Any ideas on how I could deal with this?
I have 100+ GB of free space storage, btw, 2.6 GHz intel core i7 and 16 GB memory.
Internal drive: PCI-Express Internal Physical Disk • GUID Partition Map

 

[Fastsavage]

I think you need to convert your drive format to APFS

Use Disk utility and select your drive - go to the edit menu and convert to APFS

 

[Leon.De.La.Rosa]

The option is grayed out, not available. . Do you think that if I do a clean install from a bootable drive, that will work? I do have everything backed up onan external drive through time machine, but clean installs always give me the creeps.

 

[MarkC426]

It sounds like something else is wrong.
You should still be able to connect to the App Store that is in High Sierra (my iPad 2 still does on ios9).

Also how big is your boot drive?
You REALLY need at least 25% free for normal usage.