Yeah most of these fans use proprietary radio modules and remotes. Most of them though use 433Mhz. Today it is easy to replicate.
Instead of replicating the RF it is much easier to build a widget taking apart the remote (they are just a bunch of on / off switches).
I am sure that you can maybe purchase a wall switch which is probably just some AC powered RF device on the wall; well similar to your Caseta switches.
Old master bedroom ceiling fan was mounted on a vaulted ceiling. I did have to replace the control module on it once and never touched the remote control pieces of it.
If you want take one remote control apart and take pictures of it. There are only XX buttons on it such that it wouldn't be a big deal to solder 2 little wires to each switch connection.
Here mentioned a modified digital button for garage door opener which was easy with one pair of wires.
Here is a modification of an RGB controller for a combo digital dimmer and remote automated switch for my kitchen counter LED lighting. This was a PITA to do and it has worked well now for over a year.
Look here for my endeavor DIY. Note that this is using propietary WiFi / MQTT which is different than Zigbee.
Under kitchen cabinet LED lamps with mcsMQTT control
The other bedrooms had fans / light combos with wall switches which worked fine for me.
Rambling a bit here...
There are a few Lutron folks here that have probably done endeavors for their fans in their homes and lets see if they chime in.