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If it's old pine I usually use Zinnser cover stain first. 123 is water based and occasionally you get staining from the bare wood soaking through the primer. Cover stain being oil based doesn't allow this. It's a shame because 123 is also moisture vapour permeable.
The new Zinnser 123 is 123+ (or plus). It's supposed to be more resistant to this kind of staining but I've not had the chance to test it yet.
You could try using a carbide blade scraper.
It depends how hench you are, the knob on top of this one might help but it costs an extra £10, Harris do one from Screwfix for £9. Once you get the technique right you can strip a lot of paint of flat surfaces.
If you're doing mouldings one of these helps :-
If budget is an issue maybe try a butane hot airgun before you spend money on chemical stripper. They are tricky around glass as you can crack it with heat but it's less of a problem than chemical stripper on your skin which seems to happen no matter what.
IR paint stripper is end game. Speedheater Cobra is a brilliant one but spendy. If you buy one you will soon be able to sell it on here to the next person who wants one.
https://www.speedheater.com/en/product/speedheater-cobra/
https://www.youtube.com/watch?v=1kLfK0WNePM&ab_channel=Tools%26Stuff
This type of tool is good on flat surfaces. Makita make one that I have. They are very dangerous, borderline frightening.
I lent mine to my brother and he bought one when I needed it back. I prefer the ir gun because it handles mouldings which are the bane of a restorers life.