You can use software encoding. You would select "None" from the hardware acceleration drop down. Whether your old CPU is up to the task is another story.
Jellyfin 10.10.6 (Docker)
Ubuntu 24.04.2 LTS w/HWE
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
4x WD Red Pro 6TB CMR in RAIDZ1