Yes. 4s is way too long for hand holding.. Tho I just used this cheap 10 bucks random mini tripod from amazon
the only solution I have found is an app called FiLMiC Pro. Very good app, but pricey. You can always try it and refund within 48 hrs though
Oh. My phone is rooted and I bought an application in the playstore. With that you can change the shutter speed till 99 seconds and you can do bunch of other stuffs
I have a Bostionye set. I have an S20+ it works pretty well on it. The set comes with a clip. Not very expensive. Not sure how well it would work on your S21u sensors. Here's an Amazon link to the set I have.
Check it out. Maybe it will work? Congrats on the new job, good luck!
It's in the app store for free. Google software - it's actually pretty good. Or or here if you can't find it in the play store. You might have better luck with the original file instead of the compressed one I used.
Some AI enhancement could help, waifu2xWaifu2x or remini(https://play.google.com/store/apps/details?id=com.bigwinepot.nwdn.international). It's already a good photo though
Lintless cloths (Amazon link).
Tissue can be used, but most may leave small microfibers on the lense. Lint free is best.
edit: Use a circular motion when cleaning, moving center to out.
Yes. You were right in this too.
These are the apps that you can use from the developer MOBILEPHOTON