Is train ticket a valid mode of exiting Schengen as return ticket

Indian national and resident. Planning my upcoming vacation for UK and Europe. Have received a multi entry 6 month UK Visa approved and applying for Multi-entry Schengen at Germany (longest stay)

I will be starting my trip in UK, then travelling to Schengen via flight, visiting multiple countries there and finally leaving the Schengen area from Amsterdam to London via train (Eurail) with a confirmed ticket and then heading back to India. Reason for going back to London is I have family there and using it as a base for my vacation. Planned on taking the train because it’s cheaper than flights and wanted to experience the underwater train journey .

My question is will a train ticket be considered valid return ticket or will flight bookings make a stronger statement for Visa Application? If I’m travelling via train, how will immigration be done at UK entry/schengen exit?