You have 2 options here. Establish your nonprofit where your donor base is to make fundraising easier. Or establish your nonprofit where your beneficiaries are located. If these are the same country, then you’re set.
If these are difference countries then you need to figure out the pros and cons of where you get started. In general, if you’re already a resident of one of the countries that would be the place to start. Your startup expenses would be lowest as you’d have minimal travel. Plus you’d likely navigate the local administrative ecosystem easier.
If after all that you are still stuck. I’d encourage you to start where the bulk of your initial donor base will come from. It will be easier to get them to make donations if that money doesn’t have to go abroad. For countries that offer tax exemptions for donations (like in the USA) having your legal entity recognized and eligible for those exemptions make fundraising easier.
I generally encourage people with projects that aren’t capital intense (less than $20k+ to start) to just start where you are. The insights gained from being in the thick of it will save you money. They will also help you avoid mistakes. Plus the stories from your experiences will make fundraising easier.