Increasing partition size with OS on it.

The operating system already creates lots and lots of partitions. You don't need to add your own. Erase the entire hard drive and reinstall the operating system.

Please post a screenshot of what Disk Utility shows.

One would not normally have partitioned a disk with macOS Catalina or later on it. You may have a disk formatted as APFS with one container containing two volumes on it, with macOS installed in one of the volumes.

If in fact it is partitioned, you would certainly NOT "minus" (delete) the OS partition; you would delete the empty partition that is AFTER the OS partition and then expand the OS partition to the entire disk. You need to be extremely careful when doing partitioning operations especially on APFS disks.

The only way to resolve this is to remove both partitions, reformat the entire drive as APFS and reinstall macOS. I would use a bootable Monterey installer flash drive to do that, using Disk Utility from the flash drive. (For the reason that your current bootable partition is the 2nd partition on the internal drive, not the 1st partition. In this case, I cannot tell how things would work if you booted directly into Recovery Mode on the internal drive; I suspect you would not be able to remove the 2 partitions that way.)

After doing the above you will have a single APFS Container Disk utilizing all the space on the drive, and have a macOS Volume inside it. If you wish, you can then create additional Volumes inside the same Container Disk; these may be used for data or for different versions of macOS.

Be sure to back up any & all data before working on the drive.

In your case, you *CAN* resize (shrink) existing Container disk1 ... click & drag counterclockwise the grey marker dot at roughly the 10:00 position in the diagram. (The + and - signs are only used to add or delete partitions, not resize them.) Although it may be resized, I don't recommend doing it. I suggest you should remake the entire disk as above.

To repeat ... be sure to back up any & all data before working on the drive.

BTW, is this an Intel Mac or an Apple Silicon Mac?

For a few years now, using APFS, there is very little, if any, reason to partition a disk. You can have several APFS containers in the same partition, and they all share the available space on disk - so there is no longer any need to anticipate how much space will be needed, or to manually adjust partition size in Disk Utility.

Can you post a screenshot of what you see in Disk Utility?

No, creating a partition for an OS does not make it unalterable. The odd thing is why do you have an apparently non-bootable 400GB APFS container as the first position, followed by a bootable second partition; that is unusual. Did you ever have Bootcamp installed on this Mac?

It would be a good idea to have a more detailed view of your drive. Open Terminal and type the following command:

diskutil list

Post the results so we can see them. (It's just details about the drive; no personal information is revealed.)