If you are using 3.9.280 now, you can safe upgarde to latest 3.9 that is 3.9.420 first
Atleast i found 3.9.420 in repo for ubuntu focal https://packages.netxms.org/ubuntu/pool/focal/main/n/netxms/
You can also migrate the DB to a virtual server, just use a Postgresql guide on how to migrate data.
Then you have both Bare-Metal db + VM DB you can connect NetXMS server to.
You can now edit netxms Bare-Metal installation to point to VM DB (Ie Snapshot as backup), then upgrade bare-metal install to latest 4.4 stable.
Rollback plan will be to reinstall 3.9.420 and point to bare-metal db that you didnt touch
Atleast i found 3.9.420 in repo for ubuntu focal https://packages.netxms.org/ubuntu/pool/focal/main/n/netxms/
You can also migrate the DB to a virtual server, just use a Postgresql guide on how to migrate data.
Then you have both Bare-Metal db + VM DB you can connect NetXMS server to.
You can now edit netxms Bare-Metal installation to point to VM DB (Ie Snapshot as backup), then upgrade bare-metal install to latest 4.4 stable.
Rollback plan will be to reinstall 3.9.420 and point to bare-metal db that you didnt touch