Ubuntu 20.04 is the problem - it ended standard support in May 2025. The newer php packages are not available for that older OS. You won't have been receiving Ubuntu security updates either unless you added Expanded Security Maintenance (ESM).
I would recommend you urgently move to a supported OS - Ubuntu 24.04 LTS has standard support until June 2029. Then you'll get the latest php versions (note that 8.2 ends security support in 2 months, so I'd suggest 8.3 or 8.4).
It's probably easiest to spin up a new vps and then migrate sites to that.
