I don't understand the GOS strategy on its PDF viewer. It is not mandatory for an OS to provide a PDF viewer and I see the ressources are limited.
The need for a secure reader is not limited to GOS, even Samsung devices etc. could benefit from it.
The problem is that there is no secure FOSS PDF reader that is actively developed. Libera is on hold due to the war in Ukraine. MJpdf is rarely updated and the maintainer struggles to keep it listed on play store.
Given that, the best solution for me would be if the devs joined their efforts instead of continuing with several half finished products.