I remember when a startup I used to work for made the transition from svn to git. They transitioned, then threw the guy who suggested the transition under the bus; he quit, and then the company collapsed. Lol!
After I left that company I ended up at a larger company (~14k employees) in part because I'd worked on SVN-to-Git migrations before. Definitely a different beast, since there were a huge amount of workflows that needed changing, importing 10 years of SVN history (some of which used to be CVS history), pruning out VM images and ISOs that had been inadvertently added, rewriting tons of code in their Jenkins instance, etc.
All this on top of installing, configuring, and managing a geographically distributed internal Gitlab instance with multiple repositories in the tens or hundreds of gigabytes.
It was a heck of a ride and took years, but it was a lot of fun at the same time. Thankfully 'the guy who suggested the transition' was the CEO (in the first company) or CTO (in the second) nothing went wrong, no one got thrown under buses, and both companies are still doing a-okay (as far as source control goes).