From what I know, Nextcloud dropped support to 32 bit arch from version 25 but apparently support as been extended to 26 cf: https://github.com/YunoHost-Apps/nextcloud_ynh/pull/517
If you want to install version 25 on 32 bits, the testing branch warns about future incompatibilities without killing the install:
sudo yunohost app install https://github.com/YunoHost-Apps/nextcloud_ynh/tree/testing