Boar are quite big and on most driven hunts a 30 yard shot is a long shot. Most of the time sights are an irrelavance. Its much akin to shooting with a shotgun. Gun fit is a prerequisite and it should point where you look - if you look at the sights you will miss.

If you can practice on a moving target - rabbit clays are good. Failing that practice snap shooting a piecplat sized paper targets. Look at it and shoot.

Red dots take time to become familiar with. I personally don’t like them - would much rather use the rib and open sights and the sights are there to ensure good gun mount.

If I usecan optic then a proper 1-4x20 driven game scope is so much better IMHO, but not really an option on an old Rigby. You will be fine with what you already have. Besides in France many will just be using shotguns with slugs.