Unfortunately, no newer version of PHP is available within OpenWrt 19.07, which we are using. I asked in the OpenWrt packages repository, but I received no response. You can see it here:
As @viktor said, you might want to use Turris OS 6.0 (based on OpenWrt 21.02.x), which is available in one of our development branches for now.
We don’t have any plans to look at updating PHP7 or adding PHP8 to OpenWrt 19.07. We are rather focusing on polishing Turris OS 6.0.
Thank you all. Time goes and active support of php8 will be next two month, then next year of security support.
Do you know, when will be Turris OS 6.0 with OpenWrt ^21 approximately available?
On forum is announced release 5.4 last month.