Pedro-TSR has your back on this one.
For genuine ThunderBolt displays ONLY (no others) you can use the Apple ThunderBolt-3 <-> ThunderBolt-2 adapter. If the display does not have a captive lead-in cord, you will need a genuine ThunderBolt-2 cable as well.
This adapter does not pass power in either direction.
MagSafe-3 is not compatible with older MagSafe. Even if you could adapt the shape, the protocol has been updated in the later version (essentially USB Power Delivery Protocol) and the older version can't negotiate properly to get charged..