Option 1:
Use a DDNS provider like freedns.afraid.org.
Create a script to open the link.
Call the script from DHCPv6 client whenever the DCHP pool is updated.
Wireguard server runs on Mikrotik.

Option 2:
Can use Mikrotik DDNS but I never try this before since I already have a very elaborated setup before they introduce this feature.
If you just connect back to share file, Mikrotik Back To Home is just an app that abstract everything for very easy setup.

Option 3:
If you have a VPS anywhere, let that act as a Wireguard hub and everything else act as a spoke.
Benefit of this is low latency and you don't need to deal with the host of problem that comes with dynamic IPv6 prefix that infest TM.
You do need to configure each network manually in the Wireguard config.
Alternatively you can use orchestration tool like NetBird to help if you have a lot of spokes with a lot of network.

Option 4:
Use SaaS like Tailscale. Technically they are a Option 3 but it's their server instead of your server.
I never like setting my own VPN just to use third party service so I build Option 3 personally. Choose your own option, don't have to follow me.