I wasn't sure if this has been discussed yet, but with the PS5 system only a few months away, I have been thinking about this. Hopefully it can be sorted out since I plan on replacing my launch model PS4 with a PS5, and would like to continue playing pinball on it.

Also, with the higher clock frequency of the PS5, we should see see improved performance for all PS4 titles, from what I understand. They should all be running as if they were on a PS4 Pro.

This seems to explain it better:

PS5 Boost Mode & How It Affects Backwards Compatibility
While PS5 backwards compatibility has been confirmed to support nearly every PS4 title on the market when the machine launches during holiday 2020, there are issues surrounding how the PS5 will make enhancements to these games, thanks in no small part to how this new boost mode functionality works.

Long story short – by using ‘boost’ the PS5 strays away from the mode0 and mode1 emulation presets that allow it to perfectly mimic the PS4 and PS4 Pro specifications (hence the near 99% compatibility with PS4 titles on day one), forcing the console to run PS4 titles at speeds far faster than they were ever intended to.

Because of this, Sony engineers are having to work on a case-by-case basis to make select PS4 titles work with PS5’s boost spec, deciding to do this by focusing on the top 100 PS4 titles as decided by total playtime. This means while you can probably expect lots of first-party exclusives such as Days Gone, God of War and Gran Turismo Sport to be supported alongside the likes of Call of Duty, Grand Theft Auto V and Red Dead Redemption 2, many superb (but less played) titles will unfortunately not benefit from the enhanced treatment – at least not right away.
source: https://www.psu.com/news/ps5-boost-m...ps5-ps4-games/