I am able to install php7.4 on my end
┌─[root@(redacted)]─[~]
└──╼ #apt install php7.4
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
php7.4
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 40.3 kB of archives.
After this operation, 75.8 kB of additional disk space will be used.
Get:1 https://ftp-stud.hs-esslingen.de/Mirrors/archive.parrotsec.org rolling/main amd64 php7.4 all 7.4.9-2 [40.3 kB]
Fetched 40.3 kB in 1s (29.9 kB/s)
Selecting previously unselected package php7.4.
(Reading database ... 489390 files and directories currently installed.)
Preparing to unpack .../php7.4_7.4.9-2_all.deb ...
Unpacking php7.4 (7.4.9-2) ...
Setting up php7.4 (7.4.9-2) ...
However, I feel that this is related to thread #15960, the repositories are apparently inconsistent and honestly, I’d advise against installing anything until an official answer is provided, in order to prevent accidentally breaking your system.
@Development @Development-Team can you check into this?