https://www.kindacode.com/article/how-to-make-circular-buttons-in-flutter/

1. ElevatedButton

ElevatedButton의 style 속성을 이용해서 만들 수 있다.

ElevatedButton(
          child: const Text(
            'Button',
            style: TextStyle(fontSize: 24),
          ),
          onPressed: () {},
          style: ElevatedButton.styleFrom(
              fixedSize: const Size(200, 200),
              shape: const CircleBorder(), 
          ),
),

2. MaterialButton

MaterialButton(
        color: Colors.blue,
        shape: const CircleBorder(),
        onPressed: () {},
        child: const Padding(
          padding: EdgeInsets.all(100),
          child: Text(
            'A circle button',
            style: TextStyle(color: Colors.white, fontSize: 24),
          ),
        ),
)

3. GestureDetector + CircleAvatar

주의 : InkWell 이 아니라서 Ink 반응이 없다.

GestureDetector(
            onTap: () {
              print('Button tapped');
            },
            child: const CircleAvatar(
              radius: 100,
              backgroundColor: Colors.indigo,
              child: Text(
                'A Button',
                style: TextStyle(fontSize: 30),
              ),
)),

4. ElevatedButton + Container

1번에 Container를 넣어서 좀 더 커스텀하기 좋게 만든 버전

ElevatedButton(
        style: ElevatedButton.styleFrom(
            shape: const CircleBorder(), primary: Colors.red),
        child: Container(
          width: 200,
          height: 200,
          alignment: Alignment.center,
          decoration: const BoxDecoration(shape: BoxShape.circle),
          child: const Text(
            'I am a button',
            style: TextStyle(fontSize: 24),
          ),
        ),
        onPressed: () {},
)

5. ClipRRect + SizedBox + ElevatedButton

Clip 계열, ClipOval 로 바꿔서도 가능하다.

ClipRRect(
          borderRadius: BorderRadius.circular(120),
          child: SizedBox(
            width: 240,
            height: 240,
            child: ElevatedButton.icon(
              icon: const Icon(
                Icons.camera,
                size: 40,
              ),
              label: const Text(
                'Camera',
                style: TextStyle(fontSize: 25),
              ),
              onPressed: () {},
            ),
          ),
),

https://dartpad.dev/?id=4c31fe91ccd19e0c168f809a7fe53f81