If you find several similar/identical brands that are trademarked, they might pose a threat to your registration under some conditions.
The brands in question must operate in the same or an adjacent sector (i.e. they are both attracting the same customers with related goods and services) to be able to oppose your application based on similarity. However, anyone can challenge your application on absolute grounds, in case they view your trademark as too generic or lacking distinctiveness.
In case the similar/identical brands you found operate in completely different sectors than your brand, you don’t have to be worried about receiving opposition. For example, if you sell clothes and your competitor with an identical name sells light bulbs, they technically can file the Notice of Opposition, but it would be very complicated for them to prove a likelihood of confusion (as the goods are completely different and unrelated).