Unfortunately, it seems like Lunu's 24-word BIP39 recovery phrase although valid, uses its own unique derivation path and there's no documentation about it.
I tried to restore my test wallet using common paths and none generated the correct receiving address.
The Lunu wallet didn't look convincing to me but that is purely stupid from them and a big red flag. They deserved to become decomissioned. It's already dumb to use some non-standard derivation path but not to document some crazy unique derivation is ... (I have no polite words for this).
Thanks everybody for the help this option worked out
Excellent, good to read. Do you mind to describe a little more in details what finally helped you?
I assume you were able to export your private key in WIF format and not in raw HEX format which would require an additional conversion step to import the key into Electrum.
The Electrum private key import dialog actually explains the required key prefixes for specific address types:
WIF keys are typed in Electrum, based on script type.
A few examples:
p2pkh:KxZcY47uGp9a... -> 1DckmggQM...
p2wpkh-p2sh:KxZcY47uGp9a... -> 3NhNeZQXF...
p2wpkh:KxZcY47uGp9a... -> bc1q3fjfk...
And
p2pkh:5HpHagT65TZ... is possible for uncompressed private keys in WIF format giving you uncompressed legacy public address.