Is Using a Custom-Made Thick Cable Safe for Connecting Both Washing Machine & Dryer?

Since I have one socket in the bathroom, and replacing it with a double one will not help much (the cables are too short), and running additional cables is not necessary, I have the washing machine and dryer connected to one extension cord. While everything is fine when using one device, when two devices are turned on at the same time, the cable heats up significantly. I tested several different extension cords with a load capacity of 3000 - 3500 Watts, but each of them gets hot, to a greater or lesser extent. The question now is, if I assemble an extension cord with cables of a thickness comparable to those installed in the walls, will they heat up? Wouldn`t this then transfer to the contacts in the socket and extension cord?

The contacts in the socket are probably already heating up and the cable is getting warm because copper is a good conductor of heat as well. standard sockets have a load capacity of 10A, better ones have a load capacity of 16A

Extension cords on the market are about 1 to 1.5 mm square.
So if you connect a washing machine with a heater, probably 2500 W + a dryer with 800 W, the cable will heat up.
Check if the extension cord is not coiled because it will heat up even more.
Solution - buy a 2.5 mm cable and make an extension cord yourself

It can not be like that.
Are you doing any renovation or something soon? Then connect two separate circuits to the switchboard.

A dryer (a clothes dryer) is not 800 W but about 3000 W. Washing machine 2500-3000W.
The hair dryer is 2000W.

If you use an extension cord, you are asking for a fire. Even with just one device used at a time. A home-made extension cord is only suitable for one thing, if it is made of 3x2.5mm2 wire.
Even if there is a 2.5 mm2 cable in the wall, it is good for a load of 16A (let it be 19.5A). And here you have over 25A. If it is to be as it should be, then only separate circuits for the switchgear.

If you want to use 2 devices at the same time, buy 2 extension cords: 1 for the socket in the bathroom and 2 for the socket in the hall. This is troublesome, but the only solution for a short period of time.