Is it permissible to pray in a shirt whose sleeve has been cuffed and secured by sewing? And is it considered cuffed after it has been sewn?

It has been established that there is a prohibition against folding clothes during prayer. "Folding" (kaft) means gathering or pulling together. The majority of scholars disliked folding for the worshipper, whether done during prayer or before it, and they agreed that it does not invalidate the prayer.

What you did, which is shortening the sleeve end by sewing, does not fall under the forbidden folding, because it is a shortening of the sleeve end and not a folding of it for the sake of prayer. Folding a sleeve for the sake of prayer falls under the prohibition, but if it is folded beforehand for work or due to excessive sweating, it is not disliked.