@Harmanjeet Singh
To clarify @Vasilev's informative post about opening and running a business in Bulgaria. While the business itself can be run by non-EU citizens, this is separate from your residence status. You can, of course, use your Singapore passport to stay visa-free in Bulgaria for up to 90 days in 180, which might well be sufficient, if you have a trustworthy manager and/or you choose a more passive investment (such as property). And you can rent or buy a property even as a tourist. If you need to stay longer, then a residence permit would be necessary. A very popular option, as mentioned in his post, is based on your existing overseas business using the TRO (Trade Representative Office). I believe that @Vasilev, as a business-oriented immigration attorney has done a lot of these over the years!
More generally, Bulgaria is a member state of the EU, so it can be viewed as both an independent market, and a gateway to the rest of the EU. Especially as the EU has a number of regulations relating to business "passporting", which means that a Bulgarian company can trade throughout the EU. And, typically, if it's some kind of regulated business that has been approved by the relevant Bulgarian authorities, that approval applies in the rest of the EU too.
It's also the lowest cost (including property), the lowest tax (10% flat rate), and lowest wage member of the EU, so this means it's typically one of the cheapest places to start and run a business. These advantages mean that many large European (and non-European) businesses frequently choose Bulgaria as a manufacturing, service, or logistics hub.
The "gateway" aspect also applies to personal residence, as EU rules support the granting of permanent residence after 5 years. And this permanent residence is much more durable than is commonly issued by non-EU countries (and many countries won't ever give PR status regardless of length of residence). The Bulgarian (or other EU) PR does not confer automatic migration rights (although it can do, under the EU Long Term Resident's Residence Permit option). But most EU countries do, in fact, make it relatively easy for PRs from another EU country to relocate.
Or, you can simply be a PR in Bulgaria and use your 90 in 180 allowance in other EU countries. This is made very convenient by frequent low-cost airline connections (e.g. Ryanair, Wizzair), and use of Bulgarian registered cars, Bulgarian driving license, and Bulgarian EHIC (health card) elsewhere in the EU.