Not sure why you're not seeing any update available for J4 let alone one for 3.10.12. Perhaps rebuild the update server list in the Joomla update component.
The blank pages are an indication of PHP errors. Turn on error reporting and debug to get fuller details of the errors (suspect as you do that they would relate to your template).
J4's minimum PHP is 7.2.5 (but you shouldn't be using ANY 7.x series these days.). Joomla 4's recommended version is PHP 8.2.
However, as I recall, Joomla 3.10 minimum is PHP 5.3.10 but the 3.10 series I believe runs OK on earlier versions of PHP 8.0/8.1(but not 8.2). Of course, this will also depend on 3rd party extensions which may not require or match Joomla's standard for minimum or recommended requirements. You may need to temporarily reduce the PHP version to whatever the lowest version your host allows you to select (e.g. in cPanel, some hosts may still allow PHP 7.4.x).
The fact your template bombs out with PHP 8.1 tells me you need to update that template or seek an alternative.
To be safe, for the migration itself, the best advice is to set it to Protostar to accomplish the migration from 3.10 to 4.x (J4's default template is Cassieopia, in place of Protostar this will be done as part of the migration). Then you can seek a new template or an update to your existing template for J4.
I believe, that if your hosting doesn't match the minimum requirements, it will (or should) not show the update being available, but this seems unlikely here, you wouldn't be using anything less than PHP 7.2 would you?
You could try to migrate the site offline, using a local host server such as WAMPServer, which gives you some flexibility on the choice of PHP versions and you can install different versions to suit your needs. (https://wampserver.aviatechno.net/ for downloads).
Test-drive the migration locally rather than on your production site. Then you can transfer that local copy back to your live server using Akeeba Backup/Kickstart (the often recommended method on this forum for copying/moving a website between servers. (https://docs.joomla.org/Copying_a_Joomla_website).
The blank pages are an indication of PHP errors. Turn on error reporting and debug to get fuller details of the errors (suspect as you do that they would relate to your template).
J4's minimum PHP is 7.2.5 (but you shouldn't be using ANY 7.x series these days.). Joomla 4's recommended version is PHP 8.2.
However, as I recall, Joomla 3.10 minimum is PHP 5.3.10 but the 3.10 series I believe runs OK on earlier versions of PHP 8.0/8.1(but not 8.2). Of course, this will also depend on 3rd party extensions which may not require or match Joomla's standard for minimum or recommended requirements. You may need to temporarily reduce the PHP version to whatever the lowest version your host allows you to select (e.g. in cPanel, some hosts may still allow PHP 7.4.x).
The fact your template bombs out with PHP 8.1 tells me you need to update that template or seek an alternative.
To be safe, for the migration itself, the best advice is to set it to Protostar to accomplish the migration from 3.10 to 4.x (J4's default template is Cassieopia, in place of Protostar this will be done as part of the migration). Then you can seek a new template or an update to your existing template for J4.
I believe, that if your hosting doesn't match the minimum requirements, it will (or should) not show the update being available, but this seems unlikely here, you wouldn't be using anything less than PHP 7.2 would you?
You could try to migrate the site offline, using a local host server such as WAMPServer, which gives you some flexibility on the choice of PHP versions and you can install different versions to suit your needs. (https://wampserver.aviatechno.net/ for downloads).
Test-drive the migration locally rather than on your production site. Then you can transfer that local copy back to your live server using Akeeba Backup/Kickstart (the often recommended method on this forum for copying/moving a website between servers. (https://docs.joomla.org/Copying_a_Joomla_website).
Statistics: Posted by AMurray — Wed Feb 07, 2024 9:55 pm