6502 is a bit limited, so you'd have to resort to self-modifying code to get things done — and self-modifying code is a big no-no on any processor with cache, and therefore not a good habit to acquire.
For teaching, I would instead go with RISC-V. In particular RISC-V with the bitmanip extensions, which make some things much easier and gives it feature-parity with the base set on x86 and ARM.
The Raspberry Pico 2 has two RISC-V CPUs with those. The board is easy to use, widely available and has a lot of support. There are also alternative boards with the same MCU but other form factors and features.
For teaching, I would instead go with RISC-V. In particular RISC-V with the bitmanip extensions, which make some things much easier and gives it feature-parity with the base set on x86 and ARM. The Raspberry Pico 2 has two RISC-V CPUs with those. The board is easy to use, widely available and has a lot of support. There are also alternative boards with the same MCU but other form factors and features.