I don’t know since, but testTagsAsResourceId is available as part of androidx.compose.ui.semantics package in Compose. According to the description, the value will be available as AccessibilityNodeInfo.viewIdResourceName.
This is brilliant news since UIAutomator can access the element via resource id as before, via accessibility tree-based integration test such as Appium/UIA2 driver.
testTag is via extras. Now, Appium/UIA2 can get the extras in XPath, but the extras return all of the available attributes via the extras. It is not the best.
Resource id in Appium/UIA2 autocomplete its package name like com.package.name/com.package.name.resource.id. The testTagsAsResourceId does not need to follow the rule. It means you can specify the resource id without the package name. Appium/UIA2 expected the package name existed, or it should have been there. Thus, Appium/UIA2 automatically appended the possible package name if the given query did not have it.
disableIdLocatorAutocompletion settings API in Appium/UIA2 can disable such autocomplete feature. It helps to find an element with find_element :id, 'someting' without a package name in the compose case.
~ my tech diary ~ 