Ps 1.6.1.4 - update version php 7.4

[inkout]

Hello ,
one of my clients has prestashop at version 1.6.1.4.
I received an email from my hosting that I will do a php upgrade to version 7.4. Obviously PS 1.6 has major problems with this version of php. I tried to manually change the php version and I have errors on the following files:
Adapter / Adapter_EntityMapper.php (line 71 and 84)
classes / modules / Module (line 290)

The problem is array_key_exists with objects. Following the php documentation I put propriety_exists or isset. In this case the error disappears but I have an error with the variable $ id_shop (which cannot be accessed). Do you have any idea how to do it? Or do I necessarily have to upgrade to PS 1.7? Thank you

[musicmaster]

I would at least update Prestashop to 1.6.1.24.That is a bit more solid - but even that isn't recommended for PHP versions newer than 7.1.

Even the newest Prestashop version (1.7.7) is only compatible with 7.3. Some people run it with 7.4, but that goes beyond the specifications and others downgrade because of the resulting problems. Only Prestashop 1.7.8 will be fully PHP 7.4 compatible.

An alternative is the Prestashop clone Thirty Bees that continues the PS 1.6 line and has made it compatible with PHP 7.4.