There are a few considerations that need to be made into selecting a microcontroller itself, rather than the dev board. Assuming the project contains fully custom electronics, there is no limitation on the exact MCU chosen as there would be if you were only selecting between dev boards. Students and hobbyists sometimes artificially limit themselves even further, sometimes staying loyal to certain ecosystems and only selecting from dev boards within those ecosystems (such as Arduino or mBed). While there is certainly nothing inherently wrong with any of the ecosystems, you'll fail to grow as a professional engineer if you're incapable of considering other solutions or appreciating the unique strengths each piece of hardware brings to a particular project.
United States
Great Britain
India
Germany
France
Canada
Russia
Spain
Brazil
Australia
Singapore
Hungary
Ukraine
Luxembourg
Estonia
Lithuania
South Korea
Turkey
Switzerland
Colombia
Taiwan
Chile
Norway
Ecuador
Indonesia
New Zealand
Cyprus
Denmark
Finland
Poland
Malta
Czechia
Austria
Sweden
Italy
Egypt
Belgium
Portugal
Slovenia
Ireland
Romania
Greece
Argentina
Netherlands
Bulgaria
Latvia
South Africa
Malaysia
Japan
Slovakia
Philippines
Mexico
Thailand