Looks good, a lot of the comments are superficial/nitty.

Reviewed 4 of 4 files at r1, 4 of 4 files at r2, 4 of 4 files at r3, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @dt and @postamar)

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/helpers.go line 60 at r2 (raw file):

}

func undroppedElements(b BuildCtx, id catid.DescID) ElementResultSet {

Nit: Might be a bit cleaner to have a comment on this one its a shared helper function. Though we aren't good with that convention.

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/helpers.go line 98 at r2 (raw file):

	})
	if name == "" {
		return fmt.Sprintf("%s #%d", typ, id)

It feels like there should be something stricter, but I don't think there is a nice solution here. i.e. For any new element types that are missing logic in here.

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/helpers.go line 117 at r2 (raw file):

// CASCADE.
func dropCascadeDescriptor(b BuildCtx, id catid.DescID) {
	undropped := undroppedElements(b, id)

Nice, much cleaner than the old pattern!

pkg/ccl/backupccl/backup_test.go line 7851 at r1 (raw file):

		{
			const re = `type .* is offline|relation .* is offline|cannot drop a database or a schema with OFFLINE`
			sqlDB.ExpectErr(t, re, `DROP TYPE newdb.sc.typ`)

Nit: Might be just cleaner to embed the individual for the first two, there is no real commonality except for the last one.

Reviewed 4 of 4 files at r1, 4 of 4 files at r2, 4 of 4 files at r3, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @dt and @postamar)

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/helpers.go line 74 at r2 (raw file):

}

func errMsgPrefix(b BuildCtx, id catid.DescID) string {

Can you comment the intention of this function, it's not obvious

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/helpers.go line 92 at r2 (raw file):

			typ = "type"
		case *scpb.Namespace:
			if name == "" || target != scpb.ToPublic {

this != scpb.ToPublic deserves commentary

pkg/sql/importer/import_stmt_test.go line 1231 at r1 (raw file):

				defer func() {
					_, _ = db.Exec(fmt.Sprintf("DROP DATABASE %s", dbName))
				}()

This change doesn't leave me feeling great. I understand why you're doing it: sometimes the drop is going to fail due to offline descriptors, but I have to assume that it was here for a reason. Perhaps some of it was to validate the state of the database. Maybe augment this test with a scan of crdb_internal.invalid_objects?

Code quote:

				defer sqlDB.Exec(t, fmt.Sprintf(`DROP DATABASE %s`, dbName))

thanks for fixing this.

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @dt and @postamar)

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/helpers.go line 50 at r3 (raw file):

func dropRestrictDescriptor(b BuildCtx, id catid.DescID) (hasChanged bool) {
	undroppedElements(b, id).ForEachElementStatus(func(_ scpb.Status, target scpb.TargetStatus, e scpb.Element) {
		if target == scpb.ToAbsent || target == scpb.Transient {

nit, looks like we don't need this check since everything is from undroppedElements?

pkg/sql/schemachanger/scbuild/internal/scbuildstmt/helpers.go line 62 at r3 (raw file):

func undroppedElements(b BuildCtx, id catid.DescID) ElementResultSet {
	return b.QueryByID(id).Filter(func(current scpb.Status, target scpb.TargetStatus, e scpb.Element) bool {
		if target == scpb.InvalidTarget {

could you add a comment that why target ==scpb.InvalidTarget indicate a non-public element?