I tried the new Android client using a Pixel 7a running Android 15beta (resolution 1080 x 2400 pixels). The e-mail display is too small to read with ease.
As a minimum there needs to be an option to change the font size and typeface and preferably to customise many other individual components of an e-mail.
To increase the font for reading messages or to change the font for reading messages on Android OS14 official release version, see my post in the following thread.
Note: If that doesn’t work on your Droid OS15 Beta, then could be a Droid OS Beta issue.