What am I looking for if I need to replace a "Water Supply Hose type 3/4”-G"? Google does not return much for this keywords

[Mini Me]

Turns out that the hose is too short ...if it was longer for this situation
Installing an elbow there would result in a weird position and location for what is there right now.
To make it look decent I would need to remove that cover that you see there and install the elbow close to the wall
The shoot off valve and its adapter will run horizontally parallel with the wall it will get into the space behind the toilet
There I could support the join between the shutoff valve and the hose ...
But then I have to tile hole exposed .... grrr

 

[Mini Me]

How about G Thread (Metric BSPT) Male to NPT Thread Female Pipe Fitting Adapter - Lead-Free Adapter (3/4 to 1/2 inch)

https://www.amazon.com/Thread-Metric-Female-Fitting-Adapter/dp/B07JZVVRFR?th=1

There are other variations, but that seems like the one you might want.

this could allow me to find a hose that is more common here in North America but it will add to the too much weight already on the pex pipe

 

[Sponsor]

 

[Mini Me]

Assuming the pressure gauge is reading accurately, your water pressure is too high. The pressure supply to a home should not exceed 80 psi and most municipal water supply pressure is 60 psi which is more than sufficient unless the building is a high rise. High rise buildings will usually utilize booster pumps to ensure sufficient pressure is supplied to upper levels.

If your water is supplied by your own private well, then your pump's pressure switch setting adjustment should be reduced. If your water supply is municipal, you will require a pressure reducing valve located as close as possible to where the supply line enters your home.

I don't know what to think because if I turn any tap on upstairs there is not enough pressure downstairs (basement) to feed a second opened tap
That means that gauge is crap ??
The entire house is 1/2" copper except some segments in this new bathroom where I put 3/4" pex for the cold supply that feeds the sink and the toilet+shower in this bathroom I am working on
I think it is the same (1/2" copper) from the street , common problem here in Toronto with the old houses, the plumbing was done to supply just one floor

 

[Reach4]

this could allow me to find a hose that is more common here in North America but it will add to the too much weight already on the pex pipe

As I think I see it, that adapter converts your big chrome piece to effectively have a 1/2 FIP input. So whether that weight is take by the PEX or is hidden behind the toilet, you have a choice.

You could put a 3/8 output sharkbite right angle valve at the wall. Then run a 3/8 compression supply line from there to behind the toilet.

 

[Bannerman]

In have seen older city homes equipped with 1/2" supply lines from the street. While not ideal, they typically did not experience problems supplying one or two fixtures at the same time.

Most faucets are supplied through 3/8" flexible supply lines, but the bathtub faucet and outside hose bib will usually be connected with 1/2" pipe directly and so full flow to those faucets maybe more likely to reduce the flow rate to other faucets.

Since in your case, opening a faucet on the lower level results in sufficient pressure drop to cause flow to cease to upper level faucets, I suspect a flow restriction such as the main valve which may not be open fully or is broken internally, thereby reducing the flow rate through the valve.

Another possibility is a water softener which contains damaged resin (common with chlorinated municipal water) which is causing a flow restriction. If that is the cause, as a simple test method, bypassing the softener should immediately increase the flow rate, likely restoring flow to upper faucets at the same time a lower level faucet is open.

A flow restriction does not explain the pressure gauge reading 90 psi. Either the pressure from the city is actually 90 psi static pressure (while no fixtures are flowing), or that pressure gauge is not indicating the correct pressure.

Utilizing a standard chrome toilet supply angle stop and braided supply line as suggested earlier, should result in the installation appearing correctly and not as a hacked together DIY installation.

 

[Mini Me]

In have seen older city homes equipped with 1/2" supply lines from the street. While not ideal, they typically did not experience problems supplying one or two fixtures at the same time.

Most faucets are supplied through 3/8" flexible supply lines, but the bathtub faucet and outside hose bib will usually be connected with 1/2" pipe directly and so full flow to those faucets maybe more likely to reduce the flow rate to other faucets.

Since in your case, opening a faucet on the lower level results in sufficient pressure drop to cause flow to cease to upper level faucets, I suspect a flow restriction such as the main valve which may not be open fully or is broken internally, thereby reducing the flow rate through the valve.

Another possibility is a water softener which contains damaged resin (common with chlorinated municipal water) which is causing a flow restriction. If that is the cause, as a simple test method, bypassing the softener should immediately increase the flow rate, likely restoring flow to upper faucets at the same time a lower level faucet is open.

A flow restriction does not explain the pressure gauge reading 90 psi. Either the pressure from the city is actually 90 psi static pressure (while no fixtures are flowing), or that pressure gauge is not indicating the correct pressure.

Utilizing a standard chrome toilet supply angle stop and braided supply line as suggested earlier, should result in the installation appearing correctly and not as a hacked together DIY installation.

I think that you are correct it is 90psi static. At the moment when I measured that nothing else was opened in the house.

I will go down the 3/8 hose route (option2)

I also noticed that the manual mentioned in the first post lists this as included

7/8” Ballcock to 3/4”-G Bushing Filter

 

[Mini Me]

Guys many thanks and may you reach the Plumbers' Heaven/Paradise ) for all the help provided