Thank you for all the answers.
For information, the Pi Zero 2W is 64N with 512K of memory.
I used it in 64B version in lite version without screen.
I installed a cooler and its temperature is around 42°C on average. So there is no overheating.
Diagrams over several days show no overhead and no memory overflow. As a precaution, I modified the swap to 1024 instead of the original 256 but without any change!
Syslog and usersylog don't show anything special. Pi seems to completely crash and stop. No more SSH or HTTP connection and Weewx no longer records anything on the shutdown period.

User LOG :
Oct 2 01:10:54 RPi-Meteo weewx[601] INFO weewx.cheetahgenerator: Generated 2 files for report wxobs in 0.32 seconds
Oct 2 01:10:54 RPi-Meteo weewx[601] INFO weewx.reportengine: Copied 0 files to /var/www/html/weewx/wxobs
Oct 2 01:11:14 RPi-Meteo weewx[601] INFO weewx.reportengine: ftpgenerator: Ftp'd 78 files in 19.97 seconds
Oct 2 01:15:18 RPi-Meteo weewx[601] INFO weewx.manager: Added record 2022-10-02 01:15:19 CEST (1664666119) to database 'cmon.sdb'
Oct 2 01:15:18 RPi-Meteo weewx[601] INFO weewx.manager: Added record 2022-10-02 01:15:19 CEST (1664666119) to daily summary in 'cmon.sdb'
Oct 2 01:15:26 RPi-Meteo weewx[601] INFO weewx.manager: Added record 2022-10-02 01:15:00 CEST (1664666100) to database 'weewx.sdb'
Oct 2 01:15:26 RPi-Meteo weewx[601] INFO weewx.manager: Added record 2022-10-02 01:15:00 CEST (1664666100) to daily summary in 'weewx.sdb'
Oct 2 01:15:27 RPi-Meteo weewx[601] INFO weewx.restx: WeatherCloud: Published record 2022-10-02 01:15:00 CEST (1664666100)
Oct 2 01:15:27 RPi-Meteo weewx[601] INFO user.historygenerator: historygenerator.py: Generated 6 tables in 0.29 seconds
Oct 2 01:15:30 RPi-Meteo weewx[601] INFO weewx.restx: Wunderground-PWS: Published record 2022-10-02 01:15:00 CEST (1664666100)
Oct 2 01:15:32 RPi-Meteo weewx[601] INFO weewx.cheetahgenerator: Generated 10 files for report SeasonsReport2 in 4.78 seconds
Oct 2 01:15:34 RPi-Meteo weewx[601] INFO weewx.imagegenerator: Generated 20 images for report SeasonsReport2 in 2.16 seconds
Oct 2 01:15:34 RPi-Meteo weewx[601] INFO weewx.reportengine: Copied 0 files to /var/www/html/weewx
Oct 2 01:15:34 RPi-Meteo weewx[601] INFO weewx.cheetahgenerator: Generated 1 files for report Inigo in 0.38 seconds
Oct 2 01:15:34 RPi-Meteo weewx[601] INFO weewx.reportengine: Copied 0 files to /var/www/html/weewx/ss
Oct 2 01:15:35 RPi-Meteo weewx[601] INFO weewx.cheetahgenerator: Generated 2 files for report SteelSeries in 0.19 seconds
Oct 2 01:15:35 RPi-Meteo weewx[601] INFO weewx.imagegenerator: Generated 11 images for report SteelSeries in 0.92 seconds
Oct 2 01:15:36 RPi-Meteo weewx[601] INFO weewx.cheetahgenerator: Generated 1 files for report cmon in 0.04 seconds
Oct 2 01:16:01 RPi-Meteo weewx[601] INFO weewx.imagegenerator: Generated 32 images for report cmon in 25.31 seconds
Oct 2 01:16:01 RPi-Meteo weewx[601] INFO weewx.cheetahgenerator: Generated 2 files for report wxobs in 0.32 seconds
Oct 2 01:16:01 RPi-Meteo weewx[601] INFO weewx.reportengine: Copied 0 files to /var/www/html/weewx/wxobs
Oct 2 01:16:28 RPi-Meteo weewx[601] INFO weewx.reportengine: ftpgenerator: Ftp'd 82 files in 26.84 seconds
----------------------------- CRASHES
Oct 2 07:17:11 RPi-Meteo mtp-probe: checking bus 1, device 3: "/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.1"
Oct 2 07:17:11 RPi-Meteo mtp-probe: bus: 1, device: 3 was not an MTP device
Oct 2 07:17:11 RPi-Meteo mtp-probe: checking bus 1, device 5: "/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.4"
Oct 2 07:17:11 RPi-Meteo mtp-probe: checking bus 1, device 4: "/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.3"
Oct 2 07:17:11 RPi-Meteo mtp-probe: bus: 1, device: 5 was not an MTP device
Oct 2 07:17:11 RPi-Meteo mtp-probe: bus: 1, device: 4 was not an MTP device
Oct 2 07:17:11 RPi-Meteo udisksd[393]: udisks daemon version 2.9.2 starting
Oct 2 07:17:12 RPi-Meteo udisksd[393]: failed to load module mdraid: libbd_mdraid.so.2: cannot open shared object file: No such file or directory
Oct 2 07:17:12 RPi-Meteo udisksd[393]: Failed to load the 'mdraid' libblockdev plugin