1.You could try to use flow to publish the PowerApps.
References:
Use flow to publish your PowerApps on a regular basis
Publish all PowerApps using flow
2.Within the "modern" UI of SharePoint Online, most of those customizations are no longer available. Fortunately, SharePoint Framework extensions enable you to provide similar functionality in the "modern" UI.
In the following tutorial, you could learn how to migrate from the old "classic" customizations to the new model based on SharePoint Framework extensions.
Reference:
Migrating from JSLink to SharePoint Framework extensions
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