Injection molding

Don't you also need to regulate the temperature via a relay that controls a heating element of some sort?

I guess it really depends on whether the OP is better with computers and software or discrete components.

A comparator and a 555 timer, adjusted by a potentiometer would suffice.

One of these could be useful (though they might just be total worthless garbage, it's hard to tell):
www.aliexpress.com/item/1005006797695369.html
www.aliexpress.com/item/1005007341104525.html

The Linuxcnc-RIO\riocore has a max6675 plugin.

github.com/multigcs/riocore/blob/main/ri...ns/max6675/README.md

4 X max31855 or max6675 will read the thermocouples of heaters
and linuxcnc will do the pid driving solid state replays for temperature regulation. I plan to use an sbc like rpi5 or opi5 with touch screen.
Now for plastic dosing the are mechanical regulators with switches
that the plan is to replace with linear encoders or linear sensors measuring distance and limit switches replaced by photoelectronic or induction sensors.
An sbc like rpi5 or opi5 will be enough using GPIO headers
and 24v breakout board for driving electro valves ?

Also am looking if it is possible to remove all hydraulic system
and convert it to pure electric machine with servomotors
because mold locking is done with toggle mechanism.

I really don't recommend you remove the switches or the hydraulic system.

Hydraulics are good (and quite expensive).

Photoelectric sensors burn out eventually, but switches last almost forever if they aren't really switching any current.

Solid-state stuff is generally not dramatically better than an equivalent mechanical option.

A fast SSD is marginally better than a fast HDD most of the time.

A mechanical relay can do almost everything a SSR can do, with only slightly higher power consumption, for a fraction of the price.

There's definitely a reason most constuction machinery is hydraulic; hydraulics are expensive, compaines would use cheaper options if hydaulics weren't so good.

"An sbc like rpi5 or opi5 will be enough using GPIO headers
and 24v breakout board for driving electro valves ?"

Be sure to check the total source and sink current limits of the RPi.

Even if each output draws very little current, if you have 20 outputs, that can add up to a lot in total.

3V relay that can be controlled by a Pi (if current sourcing limits permit):
www.lcsc.com/product-detail/C136110.html
www.lcsc.com/product-detail/C133323.html

I bought similar relays (same company) and its 5V, 12V, and 24V variants and they were all good, though a bit audibly noisy.