As per title
Hi @JackW97,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Sealing gaps between tiles and different materials is always done with flexible sealants, usually silicone, as it allows for slight differences in the expansion and contraction of materials.
In this case, I'd suggest using a suitably coloured wet area silicone such as https://www.bunnings.com.au/sika-300ml-white-sikaseal-kitchen-and-bathroom-silicone-sealant_p1210308 .
You can follow https://www.bunnings.com.au/diy-advice/diy-skills/tiling/how-to-silicone-a-gap for some guidance on the application process. Make sure you give the gap a good clean and it is perfectly dry before applying your silicone.
Let me know if you have any further questions.
Jacob