So my late uncle was working at Siemens and had a “little” home workshop/lab with resistors, capacitors, ICs, switches, soldering boards, wires and what there is. He learned something regarding radio (german: Nachrichtentechniker I think). Among others there was a self built radio clock (that got quite warm, plugged it out bc of safety concerns)

Now I am getting into microelectronics and roughly know what there is. But I only know that I should not use the leaded soldering tin (bc lead) - is there anything else that is unsafe because of old standards or aging? What should be safe to use?