The Apple standard for its built-in hardware-accelerated displays, makes them suitable for full-motion video for production/display of cinema-quality video with NO dropped frames, and NO dropouts or partial-blank scan lines due to memory under-runs or other issues. This requires a hardware rasterizer/display-generator for each fully-accelerated display, supported by Huge memory bandwidth to refresh each display 60 or more times a second.
If you need more hardware-accelerated displays than the built-in and ONE external display, and an un-accelerated iPad if desired, you probably need a more capable computer.
MacBook Pro M3 (base) models with 14-in display supports the same ONE external display.
On the MacBook AIR M3 (base) models with 13-in or 15-in displays, you can close that lovely display you paid dearly for, and use the display generator for a second external display, INSTEAD OF (NOT in addition to) the Internal display.
M4 (plain) supports up to Two fully hardware-accelerated external displays (three for Mac mini)
If you are doing ONLY program listings, spreadsheets, stock quotes and other slow to change data, there are some other solutions, but they require you to make some strong compromises.