Anyone who speaks in a tongue EDIFIES themselves

[TonyChanYT]

1 Corinthians 14:

4 Anyone who speaks in a tongue edifies themselves, but the one who prophesies edifies the church.

edifies
οἰκοδομεῖ (oikodomei)
Verb - Present Indicative Active - 3rd Person Singular
Strong's Greek 3618: From the same as oikodome; to be a house-builder, i.e. Construct or confirm.

HELPS Word-studies

3618 oikodoméō (from 3624 /oíkos, "a house" and domeō, "to build") – properly, to build a house (home, edifice); (figuratively) to edify – literally, "build someone up," helping them to stand (be strong, "sturdy").

Later verses provide further insights:

13 For this reason the one who speaks in a tongue should pray that they may interpret what they say. 14For if I pray in a tongue, my spirit prays, but my mind is unfruitful.

Praying in a tongue is fine but don't neglect to pray in a natural language.

15 So what shall I do? I will pray with my spirit, but I will also pray with my understanding; I will sing with my spirit, but I will also sing with my understanding. 16 Otherwise when you are praising God in the Spirit, how can someone else, who is now put in the position of an inquirer, say “Amen” to your thanksgiving, since they do not know what you are saying? 17You are giving thanks well enough, but no one else is edified.

The emphasis is on the realities in the spiritual dimension. When one is truly speaking in tongues, he is communicating spiritual truths enabled by the Holy Spirit. As such, it is an exercise to strengthen his beliefs and faith. He can praise God and increase his love for God and the gospel. He is building himself spiritually so long as he is in touch with the Holy Spirit. It is a time of devotion.