Thank you so very much for your reply!
I have always removed the plug as soon as the battery percentage reached 100% so thankfully the condition of the battery is still 'normal', though I'm quite worried of leaving the "Battery Health Management" unchecked. However, I have unchecked the "optimized battery charging" and was still faced with some odd problems.
Even when I quit the program and had nothing else running it still did not charge. I even tried different cables and adapters and still had this issue. So I had to switch it on and off a few times and reset the NVRAM, SMC and PRAM (with the help of this tutorial https://www.youtube.com/watch?v=M7lgWACOcFs&ab_channel=LoFiAlpaca) and left the computer switched off whilst plugged in for a while and thankfully it charged!
Hopefully this could have at least temporarily fixed this issue, I hope there's more solutions instead of replacing the entire laptop. I will try to run diagnostics and hopefully it works!