Here's an idea: Temviewer GMBH should hold up its past commitments and not unilatterally cancel lifetime subsciptions of paying customers, trying to get them to switch to monthly subscriptions.
It would undoubtedly not destroy the company's carefully built-up reputation in a flash.
It would also not make people question the company's "beliefs" of "Customer first" and "Trust" as stated on https://www.teamviewer.com/en/company/, nor the self proclaimed policy and practice of "Continuous training to ensure compliance with applicable laws, ...to emphasize the importance of acting with integrity" on the same page.
Just an idea...