If serialized items are not showing up in the XM Cloud Content Tree, it may be that the items added are all IAR items and do not have an item in the database as a parent.

When deploying code and serialized items to XM Cloud, the process creates an items.master.xmcloudinit.dat file for the serialized items. If you are not seeing items as expected in the Content Tree (but they show up in a search for the Item ID in the tree), then you can make a package of the item parents (only, no children) and install it in XM Cloud. This will add the parent to the database and then the child items will be retrieved from IAR. During package install choose Overwrite for the parent nodes.

To restart the CM server after installing the package, just perform another deployment (like deploying the last code push again). Or, on the environment page of the XM Cloud Deploy app, choose Options >> Restart Environment.

Reference

https://sitecore.stackexchange.com/questions/31062/iar-items-invisible-in-content-tree-but-exist (Opens in new window or tab)