At my home I have a MikroTik running v7.1.1 and it has IPv6 access. When I am on road without IPv6 I would like to VPN back into it to obtain IPv6 with my iPad and MacBook. What would the easiest way to do this be?

It depends. If one static address for each device would be enough, then Wireguard could do it easily. If you'd want dynamic addresses with privacy extensions, it would need something different. I'm not sure what's best, I didn't think much about it before. Long time ago I had OpenVPN in L2 mode, that worked.

Would something like Zerotier work? Been trying a number of things with no good results.

I have no idea, I never tried it.