Raspberry Pi OS read only mode
Raspberry Pi OS system has a very nice tool that you can use to enable/disable the read-only mode at will.
sudo raspi-config
It will protect your Raspberry Pi system from corruption if you don't have a dedicated & safe powering off mechanism for the Rpi. And will extend the life of your SD card since all writes will be stored in the memory.
Then restart the system. If you need to make some changes in configuration then disable the overlay (and restart the system), apply new configuration and enable the overlay again (and restart the system).