Mr. V is correct ... in goal ... 4.x is the next 'long term support' version. IF ... IF ... one used the Moodle docs for updating via the 'long way' or since you have CLI you might be able to use the 'git' way, you could keep pace.
In a git pull on Moodle 4.0 code made just a few minutes ago:
94 files changed, 1546 insertions(+), 297 deletions(-)
And there is a new tag:
* [new tag] v4.0.1 -> v4.0.1
Meaning moodle is now 4.0.1
and in the works is a 4.1dev - not ready for production use.
Since you have just begun to use Moodle so you've not users in courses, right?
If so, you could use Softac and you should be able to select 4.0.1 from their version to install drop down menu. Then report back if successful or not.
Do a site backup first and read up on how to restore it should Softac fail.
https://docs.moodle.org/400/en/Site_backup
or
https://docs.plesk.com/en-US/obsidian/administrator-guide/backing-up-and-restoration.59256/
And again ... if using Softac, your first point of problem resolution should be:
1. provider (+Plesk)
2. Softac
3. and only IF 1 and 2 are exhausted, these forums.
If you get to #3, about the only way anyone could help is for someone to volunteer their time to login as you on your Panel to be able to 'compare' or run some php command line scripts in code/admin/cli/ ... but that would be possible only if Plesk offers a 'Terminal' icon or the ability to run a command - which Moodle will block because of it's security.
For setting up cron job, which is a *must* for Moodle, see:
https://docs.plesk.com/en-US/obsidian/administrator-guide/server-administration/scheduling-tasks.64993/
'SoS', Ken