No Problem at all 
Hmm, not sure. I use it on linux and there I open the terminal from the path where the file is and write: adb sideload e-1.8.1-s-20230203257074-dev-FP3.zip
If you want to stay on ‘dev’ then I would suggest to take S. If you think about switching to ‘stable’ then please consider that with a locked bootloader you won’t be able to sideload and are dependant on the developers to offer OS OTA upgrades. Difference between ‘dev’ and ‘stable’ are as mentioned sideloading and also some backup solutions availability, Banking apps working or others, etc. I suggest you serach the forum. There are alot fo discusions about that available