the Australian Delphi User Group has just posted a presentation I made on a zoom meeting back in March, about migrating from FMX to LCL. It's also a general primer on migrating from Delphi to Lazarus.
It goes for 2 hours, and isn't that quick, but a few members told me it really helped them understand the process and how to think about Lazarus differently. So you might find it useful.