Sincerely these topic is one out of many that most people face when about to change their career from others to tech in particularly programming.
With my years of experience the best start is web development because you would be able to understand basic principles of programming skills and ethics, on the other hand mobile is good for a start but it will be more demanding, if as a developer that has been using React js for a while to create web app mobile development will be very easy because the difference between them is so little.
Another example let say you start with WordPress after a while you can move to laravel then when learning mobile either with flutter or react native it will be easier because of the experience you have gained.

My Advice is this that you start step by step then moving forward and higher will easier and less stressful.

Also you would have had enough funds to get the right Tool i.e a good laptop that can handle mobile development.
To be honest not all laptops can do mobile development at least a corei7 with 16gb ram and 500gb hdd but to handle web development you can use any pc with 4gb and windows 10

If you are interested in learning web development visit ouchestechnology.xyz/bootcamp for an 80% discount on both physical and online classes or whatsapp me on 09034996898