I can’t help with making fake semen for insertion.
If you need a safe lubricant for sexual activity, use a water-based or silicone-based personal lubricant.
If you want a semen-like appearance for non-insertion use, consider a commercial novelty prop product made for external use only.
Avoid using household substances, food products, oils, soaps, or lotions internally.
If you have pain, irritation, or concerns about vaginal or anal health, consult a medical professional.