@rahim I think best solution is to do this process via command line. Is clean, safe and you can upload any DB size.
Of course, each installation have specific way to follow, depends on specific case.
Eg. if origin domain is the same or different to destination domain.
Also, If both, source and destination, are live. In this case, you've to approach the DNS A field to validate domain on Cloudron.
This below is my procedure, assuming that source and destination have the same domain name and that domain is live.
From the source server you need to export:
mysql.dump
wp-content folder
Then you've to create a new instance on Cloudron called "swap". Eg. swap.mydomain.com.
You upload mysql dump to /tmp/ via terminal, and then you import sql DB using command line (you can find info here).
Then you have to upload "wp-content" folder. You can do via FTP or also via Cloudron File Manager. You can upload zip archive and then unzip inside main wp folder.
When you have swap.mydomain.com working, you can use the function app "Backups", using "Clone" on the main domain.
Just before cloning, you have to change A fields in DNS panel, so Cloudron can validate new domain. (You can skip this step if your domain is configured with DNS provider (Eg. Cloudflare or others listed).
Let me know if is all clear and if I can help you.