Saw I few people with that problem on the forum already and have checked for it. In the Options/Video tab Bannerlord has AMD Radeon HD 8570D as the only card listed and thus is the one I'm using. So unfortunately this doesn't seem to be the problem. Cheers anyway.
dont give up. i have a similar laptop/system to you (mine is about 7 years old) and i can play bannerlord on medium with a solid 40fps in large battles/screen transitions instant or take a couple of seconds.
How i achieved this is by being smarter than my system. I updated drivers (sound card included), i adjusted pagefile, i got 16gb RAM, i used the AMD software to make sure its set to use my GPU, i turned off sound enhancements in my sound device, i defragged, i use performance monitors such as Orbital Advanced System Care Free which closes background programs and boosts RAM, i made sure my power options maximise performance in Control Panel, i cleaned my laptop out and reapplied thermal paste to both my GPU and CPU. The majority of people dont have to do this, but i do siince all my money goes to my ex-wife and kids as alimony and i cant afford a new laptop.
The fiddly technology here is something called "Enduro" where you system switches from the CPU to GPU. what sofware drivers do you have installed? do you have the Adrenaline 2020 drivers? They really helped my 8970m card. Maybe Bannerlord has to re-recognise your card, do this by deleting all the folders in your Documents/bannerlord/config file (the game will make new ones).
Dont give up brother. Did the Uthmani Troops give up and go home at Galipoli when the world's Great powers descended on them? Hold the line.