Hi,
The system compatibility view sys.sysindexes is still available in SQL Server 2019. Actually the system table sys.sysindexes Has been deprecated, SQL Server provides a view with the same name as this system table to be compatible with the software that uses the system table.
As stated in this MS official document about sys.sysindexes:
This SQL Server 2000 system table is included as a view for backward compatibility. We recommend that you use the current SQL Server system views instead. To find the equivalent system view or views, see Mapping System Tables to System Views (Transact-SQL). This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.