People use ideas from politics, religion and ideology when they invest their savings. I’m most familiar with liberal concepts of investment based on the environment, fair pay and health. Probably few of us understand the religious guidelines of Islam and how such folks invest when following Islamic tenets. As the number of Muslims grows it is a growing niche of the finance industry.
Islamic approved investment reduces an investor’s options. To be avoided are the industries of alcohol, tobacco, pork and immoral media like porn. Interest is seen as unjustly receiving money and doing nothing productive to earn it. To earn a return in lieu of interest, the return has to be a percentage of the profits earned when the money it put to use. Because banks do not do things in this way, they are off the approved list.
Also not approved are short selling and annuities. These are too close to gambling. In general, Muslim people do not separate the secular part of their lives from the religious as most Christians do.
From what I read, mutual funds which specialize in Islamic investment do poorly when the stock market booms but do well when it retreats. The approved firms tend to keep a lot of their assets in cash. Many of the approved firms are in Islamic countries.
There are an endless number of sites that discuss financial issues. I’m going to look for one which mixes in Islam to see how it advises the faithful.