In addition to the firmware you may have to write esp_init_data_default.bin to the end of the flash. For a 64MBit flash, the target address is 0x7fc000. Try
esptool --port COM3 --baud 115200 write_flash --erase-all --flash_size=detect -fm dout 0x7fc000 esp_init_data_default.bin
This writing of esp_init_data_default.bin has to be done only once and can be made independent from the firmware. Still you may try other variants of the -fm option.
Link for esp_init_data_default.bin:
https://github.com/espressif/ESP8266_AT/blob/master/bin/esp_init_data_default.bin
related topic in the forum: #2335 (comment)

Thank you Robert, i have tried now like the following:

esptool --port COM3 --after no_reset --baud 460800 write_flash --erase-all 0x0 ESP8266_GENERIC-FLASH_2M_ROMFS-20250415-v1.25.0.bin 0x7fc000 esp_init_data_default.bin
esptool.py v4.8.1
Serial port COM3
Connecting....
Detecting chip type... Unsupported detection protocol, switching and trying again...
Connecting...
Detecting chip type... ESP8266
Chip is ESP8266EX
Features: WiFi
Crystal is 26MHz
MAC: 18:fe:34:9d:5c:bb
Uploading stub...
Running stub...
Stub running...
Changing baud rate to 460800
Changed.
Configuring flash size...
Erasing flash (this may take a while)...
Chip erase completed successfully in 15.0s
Compressed 639680 bytes to 428052...
Wrote 639680 bytes (428052 compressed) at 0x00000000 in 9.8 seconds (effective 523.9 kbit/s)...
Hash of data verified.
Compressed 128 bytes to 72...
Wrote 128 bytes (72 compressed) at 0x007fc000 in 0.1 seconds (effective 18.9 kbit/s)...
Hash of data verified.

but it also makes the same output:
M:\Projekte\Photovoltaik\BKW_REG_V01\Micropython\Flash

esptool --port COM3 --after no_reset --baud 460800 write_flash --erase-all 0x0 ESP8266_GENERIC-FLASH_2M_ROMFS-20250415-v1.25.0.bin 0x7fc000 esp_init_data_default.bin

ets Jan 8 2013,rst cause:2, boot mode:(3,2)

load 0x40100000, len 31264, room 16
tail 0
chksum 0x7a
load 0x3ffe8000, len 1060, room 8
tail 12
chksum 0xc8
ho 0 tail 12 room 4
load 0x3ffe8430, len 1124, room 12
tail 8
chksum 0x2b
csum 0x2b
Writing init data
rf_cal[0] !=0x05,is 0xFF

ets Jan 8 2013,rst cause:2, boot mode:(3,2)

load 0x40100000, len 31264, room 16
tail 0
chksum 0x7a
load 0x3ffe8000, len 1060, room 8
tail 12
chksum 0xc8
ho 0 tail 12 room 4
load 0x3ffe8430, len 1124, room 12
tail 8
chksum 0x2b
csum 0x2b
rf_cal[0] !=0x05,is 0xFF

ets Jan 8 2013,rst cause:2, boot mode:(3,2)

load 0x40100000, len 31264, room 16
tail 0
chksum 0x7a
load 0x3ffe8000, len 1060, room 8
tail 12
chksum 0xc8
ho 0 tail 12 room 4
load 0x3ffe8430, len 1124, room 12
tail 8
chksum 0x2b
csum 0x2b
rf_cal[0] !=0x05,is 0xFF

i even tried to write it to 0x3fc000, because maybe it thinks its a 4MB flash. But it didnt work either

That looks like the "normal" boot loop error. Now try the other -fm options.
esptool --port COM3 --after no_reset --baud 460800 write_flash -fm dout --flash_size=8M 0x0 ESP8266_GENERIC-FLASH_2M_ROMFS-20250415-v1.25.0.bin 0x7fc000 esp_init_data_default.bin
The flash mode options are qio,qout,dio,dout, with the default being dio.
You do not have to erase the flash all the time.

ok i tried it again with different options:

esptool --port COM3 --after no_reset --baud 460800 write_flash --erase-all --flash_freq 80m --flash_mode qio --flash_size 8MB --verify 0x0 ESP8266_GENERIC-FLASH_2M_ROMFS-20250415-v1.25.0.bin 0x7fc000 esp_init_data_default.bin

now it works! thank you very much!!!