New uptime(1) calls sysinfo(2):
$ strace -e sysinfo uptime
sysinfo({uptime=1088088, loads=[12800, 20800, 30528], totalram=20879904768,
freeram=11266564096, sharedram=1854656512, bufferram=479453184,
totalswap=2147479552, freeswap=2147479552, procs=946, totalhigh=0, freehigh=0,
mem_unit=1}) = 0
08:44:26 up 12 days 14:14, 2 users, load average: 0.20, 0.32, 0.47
+++ exited with 0 +++
So the question is why that yields odd values on pi4.